To set the therapeutic record straight, I can date the onset of the incurable addiction that has addled my brain and proven so tormenting to my family and friends. On a balmy spring day in Cambridge 17 years ago, I sat in the Baker Library of the Harvard Business School and sifted through the labyrinthine papers of Thomas W. Lamont. As senior partner of the J.P. Morgan bank in the 1920s, Lamont -- elegant, urbane, with insinuating charm -- ruled as an unquestioned potentate of Wall Street as he decreed which sovereign states could raise money. And here I was reviewing a cache of 100,000 documents that would either be incriminating or exculpatory. By day's end, I had perused Lamont's correspondence with Nancy Astor, Charles Lindbergh and Franklin Roosevelt.

This was the first time I had ever dipped into primary documents, better known in the trade as "manuscript collections." As a self-styled historian, an old English major with a queasy sense of being a highbrow fraud with a first book contract, I felt that I had touched history -- the real, perishable stuff. That night, still agog, I telephoned my wife from Boston and confessed to something deeper than a mere thrill. After years working as a journalist, hazarding educated guesses about the dumb show of business and politics, I had the odd sensation of having burgled Lamont's office, rifled his papers, violated his privacy and unmasked his secrets. To be sure, I had duly submitted call slips, sat at my appointed chair as boxes were retrieved and handled documents as gingerly as I would saintly relics. Yet I experienced the delicious, illicit frisson of being a second-story man, a literary thief, a scholarly voyeur. There was something furtive, lawless and absolutely irresistible about the whole enterprise.

When I told skeptics at parties that I was writing a saga about a banking empire, they studied me with undisguised pity and intimated that bankers must make very dull subjects. But the Morgan partners were never boring and feigned dullness only as a shield to deter prying eyes. Their papers bulged with shocking secrets: propaganda work for the Japanese militarists, racy affairs with society ladies, sub rosa contacts with the White House and State Department. Like some crazed, feverish gambler in a Dostoyevsky tale, I could rattle off my favorite finds: Lamont to President Hoover five days before the 1929 crash: "The future looks brilliant!" Or Lamont advising Benito Mussolini to liken his invasion of Ethiopia to the heartwarming settlement of the American West.

Even the Morgan partners' most intimate possessions were neatly filed away. One day, at the University of Virginia, I was riffling through the papers of partner Edward Stettinius when I noticed a silk swatch poking from an envelope. I tugged at the fabric until I was holding aloft -- to the merriment of other readers in the library -- a handsome pair of sky-blue underwear, custom-made by a Chicago firm. In his private, orderly life, Stettinius maintained a separate underwear file, which he kept in tip-top order. Luckily for historians, the urge to preserve artifacts can be as compulsive as the corresponding urge to ferret them out.

As my friends can testify, my research disease only worsened with my second book, The Warburgs, an epic account of a German-Jewish banking dynasty that rose to power in Imperial Germany and was hounded into exile by Herr Hitler. Unlike the pristine bond paper of Morgan bankers, preserved in air-conditioned vaults, the Warburg documents in Hamburg looked like sad, haunted survivors, tattered, yellowing and blackened with soot. How they escaped the talons of the Nazis, who had "Aryanized" the Warburg bank in 1938, and how they had survived the fire-bombing of Hamburg, remain a mystery. I learned German and soldiered on with a dictionary and grammar book at my side. With my self-taught, bookish German, I couldn't even ask my way to the bathroom, but I somehow waded through documents in outmoded scripts and Gothic lettering. What sustained this madness was an urgent conviction that I was thrusting my hand into a fire and rescuing charred remnants from ruin. That's also part of the research pathology: a psychological need to arrest the inexorable decay that afflicts all human records.

Some archival finds can be easy, embarrassingly so. To expose the Morgan hugger-mugger with Mussolini, I simply looked up M for Mussolini in the beautifully organized catalogue in the Baker Library. Still, as T.S. Eliot reminded us, history has many cunning passages, and the truth is usually elusive. Initially, I balked at the prospect of reconstructing a life of John D. Rockefeller, persuaded that this famous sphinx had a mind hermetically sealed from inquiry. But the Rockefeller Archive Center had made available hundreds of thousands of letters and I imagined -- with sweaty palms, a racing pulse, a budding fever of anticipation -- that what had been opaque would now be transparent.

Rockefeller, it turned out, was as secretive in his office as in public. His enigmatic letters followed a common pattern. Seldom more than two or three lines long, they discussed vague, unspecified events in an artfully indirect manner. A typical missive: "Received your letter of the 26th. Would recommend that you proceed with all due caution. John D. Rockefeller." I began to see that Rockefeller, a master puppeteer jerking the strings of his vast oil empire, wrote letters as if they might someday fall into the hands of a prosecuting attorney. Houdini-like, he vanished inside his own prose. You pulled away one veil, then another, and you still couldn't catch him. Fortunately, Rockefeller's underlings were gabby and indiscreet, and when I found the letters that had elicited his terse directives, a vast panorama of corporate genius, machinations and mischief unfolded.

The first rule of biographical research is to scrub the slate clean and scrape away accumulated lore. As William Hazlitt said, most books are made of other books, chopped up and reconstituted. Some fictions are regurgitated so often as to assume the status of unchallengeable fact. One such myth was the notion that Rockefeller's father, William Avery Rockefeller -- a colorful bigamist also known as Dr. William Levingston -- was buried in an unmarked grave in Freeport, Ill. I accepted this as an article of faith until I stumbled upon the name of an old Freeport cemetery. On impulse, I telephoned the graveyard, got a sleepy attendant and told him he had a chance to make history. He mentioned that a Rockefeller grave had once been pointed out to him. Because it was a slow day, devoid of burials, he agreed to snoop around. Twenty minutes later, he telephoned back and said nonchalantly that he had found the grave of John D. Rockefeller's father, thus ending a mystery that had lingered for a century.

I've just published a biography of Alexander Hamilton. At first, I was disappointed that his abundant papers, 22,000 pages worth, had been collected and annotated by crack teams of scholars. This threatened to deprive me of some illicit joy, making the whole business too proper and legitimate. But there were enough compensating pleasures to gratify my guilty addiction. The illegitimate Hamilton was born on Nevis in the Caribbean and spent his adolescence on St. Croix. On Nevis, I pored over the brown, brittle minutes of colonial assemblies held 250 years ago. Before turning pages, I learned to sandwich them between two fresh sheets of white paper, lest they crumble into dust. Far more troublesome were parchment sheets perforated with hundreds of minute holes, signifying insect infestation and an irremediable loss to history.

Every biographer has serendipitous finds, the result of some unquantifiable mix of persistence, ingenuity and plain luck. While on St. Croix, Hamilton, then a frustrated young clerk, had written articles and poems for the Royal Danish American Gazette. Five years later, by a miraculous sequence of events, he was adjutant to George Washington. I wondered: Had the local paper ever covered the wunderkind's ascent? As I scrolled through the paper's microfilmed issues, starting with Hamilton's departure from St. Croix in 1773, I couldn't locate a single reference to him. Yet I noticed that a certain "Gentleman from New York" kept mailing dispatches to the paper -- dispatches that tallied perfectly with letters Hamilton was then writing to friends on the identical subjects. Voila: Alexander Hamilton had been a stringer for the Royal Danish American Gazette, a discovery that filled critical lacunae in his story.

Hamilton, a human essay machine, was the quintessential man of ideas, and so I especially treasured discoveries that concerned the small change of everyday life. Two of his sons had written hagiographic volumes about their father. Trawling through their papers, I found fugitive scraps discarded as too trivial for inclusion in the Life of a Great Man. James A. Hamilton had recorded a charming scene of his father with the French barber who came to his office each morning. More poignantly, John Church Hamilton described how the night before the duel, his father, himself an orphan, prayed and then shared a bed with a young orphan boy staying in their house. For me, such vignettes erased the distance of two centuries and brought Hamilton to life. In the end, I discovered plenty of new material about Hamilton, managed to get my hands good and dirty, fed my filthy habit and guaranteed that the research craving would come back to haunt me again and again. *