Achance encounter with an elderly black son of a sharecropper seven years ago in North Carolina changed the career of blood pressure researcher Sherman James.

James was interviewing residents of a small town for a study of high blood pressure when he came across a man named after John Henry, the legendary black steeldriver who supposedly outworked a steam drill and then died from the effort.

"We sat in his back yard under a big oak tree on a summer afternoon and talked for 2 1/2 hours," recalled James, a psychologist and professor of epidemiology at the University of North Carolina School of Public Health at Chapel Hill. "I sat absolutely in awe. It changed my life."

Under that tree, John Henry Martin told James the story of his life: How he had vowed in 1928 at the age of 21 to do whatever it took to escape the poverty-stricken life of a sharecropper. How he taught himself to read and write. How he bought a few acres of farm land and, with his wife, worked seven days a week through the 1930s and 1940s to scrape a living from that soil.

"He looked at what his father had to show for a life of hard work as a sharecropper -- no education, no money, no security, nothing -- and he said he was not going to have the same life," James said.

By middle age, John Henry Martin had achieved a small measure of the economic security his father never knew: 75 acres of farmland and a little money in the bank.

But he also had what James called "a classic profile of stress-related illness": high blood pressure, peptic ulcers and arthritis. To James, it seemed as if "the story of this one man was really the story of black Americans." He thought about the life of John Henry Martin and the legend of John Henry -- and wondered if they might help unravel the riddle of hypertension in black American workers.

Ever since, James has been researching a phenomenon he dubbed John Henryism -- the belief that one can overcome one's environment by sheer hard work and determination. Psychologists sometimes refer to it as "active coping."

John Henryism is a kind of blue collar Type A behavior, in which people relentlessly pursue the American dream against a great obstacle. "In the case of John Henry," said James, "it was the mechanical steam drill. In the case of John Henry Martin, it was the sharecropper system. In a sense he beat it, but he paid a very high price."

"Coming to terms with John Henryism means coming to terms with what work means for black Americans," said James. "Commitment to the John Henry philosophy may be part of the puzzle of trying to understand why hypertension seems to be so prevalent in low-income blacks."

To measure John Henryism in workers, James has devised a scale based on responses to a list of 12 statements, such as "Once I make up my mind to do something, I stay with it until the job is completely done," and "I like doing things that other people thought could not be done." Workers are asked whether each statement is "very true," "somewhat true" or "not true."

What is the relationship between John Henryism and blood pressure? In studies of 132 black men from rural North Carolina, James found that it depends on the worker's education and economic status.

In relatively well educated and economically secure black men, high John Henryism scores were associated with reduced risk of high blood pressure. But in poor black men, the same high scores on the John Henryism scale were associated with increased risk of high blood pressure.

In other words, the same John Henry-like drive that seems healthy in educated black men, James said, could be unhealthy in those who lacked education and money. The results, reported in the Journal of Behavioral Medicine, confirmed previous findings that education helps protect high-risk people against hypertension -- by helping them control the factors that stress their lives.

Under a grant from the National Heart, Lung and Blood Institute, James is conducting a follow-up study of the link between John Henryism and hypertension in 1,550 low-income men and women -- both blacks and whites. Results aren't expected for at least six months.

"Don't get me wrong -- I'm not against work," said James. "Work is one of the truly satisfying things in anyone's life. But there are circumstances under which hard work, even successful hard work, can have psychological and physiological effects on health."