AS MORE RECENT blood baths in Cambodia, Bosnia and Rwanda have revealed, the collective horror over the Holocaust was not enough to preclude subsequent genocidal campaigns. Yet Nazi Germany's extermination of Jews, Gypsies, gays and others remains particularly chilling, in part because of its bureaucratic means and "scientific" basis. Hitler's murderous crusade was technocratic utopianism's evil twin.

Of course, many of the assumptions underlying Nazism were not what would be called today "good science" -- impartial, verifiable, universal. In fact, many of them weren't science at all. "Deadly Medicine: Creating the Master Race," an insightful and suitably disturbing exhibition at the U.S. Holocaust Memorial Museum, doesn't emphasize the mystical side of the Nazi worldview, but doesn't entirely obscure it. Near the beginning of the show -- and just inside the comprehensive brochure that accompanies it -- is a 1911 poster for the German Hygiene Museum in Dresden. It features a large, omniscient eye, adapted from the eye of the primeval Egyptian god Ra.

Egyptian mythology, the legend of the Holy Grail and ancient India -- source of the swastika -- were all interests of the supposedly scientific thinkers who did the groundwork for Nazi eugenics. In the early 20th century, some German anthropologists began ranking the various human "races" and found the Nordic type "eugenically advantageous." Yet the term they often applied to this "master" race was "Aryan," a word that had nothing to do with northern Europe. It comes from the Sanskrit "arya," whose original meaning is a matter of ongoing debate. But it's likely that the first "Aryans" were no more blond-haired and pink-skinned than the indigenous residents of contemporary New Delhi.

"Deadly Medicine" traces the vogue for eugenics to Britain. (The term, which means "good birth," was coined by British scientist Francis Galton in 1883.) Other countries where eugenic policies were strongly advocated included Sweden, the Soviet Union, Japan and, yes, the United States. Before the Nazis took power in 1933, the only country with a national sterilization law was Denmark. But almost 8,000 people were sterilized in four California state mental hospitals between 1908 and 1933, and in 1927, the U.S. Supreme Court upheld Virginia's forced-sterilization law. Justice Oliver Wendell Holmes Jr. decreed that "three generations of imbeciles is enough," an opinion that now seems, well, not so smart.

Among connoisseurs of such things, the definition of "imbecile" and the identity of the "master race" varied according to circumstance. In Germany, the thrust of racialist thinking was to distinguish Jews from other German citizens and to prevent intermarriage between members of the two groups.

That wasn't the concern of race-minded policymakers in the American South, yet the Nazis who instituted 1935's Marital Health Law had much in common with their American cousins. A German pamphlet that warned "Don't go blindly into marriage" featured an illustration borrowed from the Louisiana Department of Health; it depicts a man and woman who appear quite similar, but intimates that one of them is somehow tainted. You gotta watch out, even if what you're watching out for is different in New Orleans than in Dusseldorf.

Ultimately, Germany's eugenic ideology became hugely destructive, but its early manifestations were often meaningless and outright silly. A 1925 "Racial Map of Europe" seems to be based on language as much as anything, and even that doesn't fully explain the categories. (Ireland and northwestern Spain are predominantly "Westische," which apparently means Celtic, but Brittany isn't.) A 1930 study purports to distinguish Jews by such genetically neutral attributes as politics and thus identifies liberal-leaning gentile Charlie Chaplin as Jewish.

Such absurdities become ominous, however, when Hitler takes power and the Nazis define Germany as what the exhibition calls "The Biological State."

Production of healthy, genetically homogeneous babies became a virtual assembly line, with Lebensborn ("fount of life") homes built to hold pregnant women. Abortion was harshly penalized, and women who had four or more children received the Honor Cross of German Motherhood. The goal was not to create better individuals, but a stronger nation. One of the "10 Commandments for Choosing a Mate" instructed that "your life is a transitory occurrence; family and nation will continue to exist."

Meanwhile, the sterilization and killing of "degenerate" and "mentally and morally subnormal" Germans began. In 1937, children of Arab, African and Asian fathers were secretly sterilized. Beginning in 1939, more than 5,000 mentally challenged or chronically ill children disappeared from state institutions. The T-4 program, begun in 1939, targeted adult mental patients, and was the first Nazi operation to massacre people in collective gassings. (By 1945, it had killed 200,000 people.) By the time it invaded Poland in September 1939, Germany was adept at mass murder and ready to turn its skills to the "scientific" elimination of the Jews -- a hygiene problem, since they supposedly "caused typhus" -- and the Slavs. (Some 3 million Soviet prisoners of war perished in German custody.) Some of the final exhibits demonstrate how Nazi abuse of science continued in death camps such as Auschwitz, where physician Josef Mengele conducted his notorious experiments. But much of that information is on permanent display in the museum. The exhibition is primarily about how Nazi Germany developed the mindset that encouraged and justified the atrocities it committed after World War II began -- how it turned eugenics from a vaguely distasteful concept into one of the monumental horrors of human history.

"Deadly Medicine" is an extraordinary and accessible -- recommended to those 11 and older -- work of scholarship. It's also a diabolically effective piece of design. The first part of the show feels unthreatening, almost antiseptic, but the galleries gradually become less inviting and more oppressive. The walls seem to be weathered, the floors dirty, suggesting the sort of poorly maintained institutions where so many innocent Germans died.

Escaping past the last display -- a gallery of murderous doctors, most of whom continued their careers after 1945 -- most viewers are likely to feel some mixture of anger and sorrow, but also relief.

DEADLY MEDICINE: CREATING THE MASTER RACE -- Through Oct. 16, 2005, at the U.S. Holocaust Memorial Museum, 100 Raoul Wallenberg Pl. SW. 202-488-0400. Open daily from 10 to 5:30, and till 7:50 Tuesdays and Thursdays to June 17. www.ushmm.org.

Nazi propaganda on the importance of preventing births among the "unfit" included a 1938 poster showing an athlete shrinking as a deformed man grows. Below, women received the golden Honor Cross of German Motherhood for having eight or more "fit" children. The head of a Jewish youth was sculpted from wood by the Jewish artist M. Winiarski for German officials in the occupied Polish city of Lodz.Tools of anthropological research, such as this eye chart, devised in 1910 by Rudolf Martin, became instruments used by eugenics advocates for measuring human worth.