Harry Levinson, a psychologist who helped change corporate America's thinking about the workplace by demonstrating a link between job conditions and emotional health -- a progressive notion when he began developing his ideas in the 1950s -- died on Tuesday in Delray Beach, Fla. He was 90.

His death was confirmed by his son Marc.

As a management consultant and an educator at Harvard, M.I.T. and other universities, and through books, seminars and his own research institute, Dr. Levinson showed how psychoanalytical theories and methods could be used to motivate employees. He was among the first psychologists to postulate a connection between thwarted career aspirations and depression.

Many of his management theories are now practically truisms. But to the gray-flannel corporate culture of the postwar years, they were novel, compelling many managers to think beyond the traditional reward system of promotions and paychecks to motivate employees.

One of Dr. Levinson's ideas, put forth in his book ''The Exceptional Executive'' (1968), held that companies must be ''learning organizations'' and that their leaders must be teachers. The concept was adopted and popularized decades later by John F. Welch Jr., the former General Electric chairman and one of corporate America's most influential leaders.

Dr. Levinson argued that a psychological contract existed between employees and employers, laying out the expectations each had of the other. Employees who feel that their employers have violated that contract will feel depressed, he said, and may well become underachievers.

He envisioned an even more dire situation in which employees despair of ever reaching their full potential -- in psychological parlance, when they face a wide gap between their self-image and their ego ideal. It did not matter if such discontented employees were reacting to workplace unfairness or to their own inherent insecurities, he said; in either case, they were likely to feel helpless and depressed, and thus be underproductive or even disruptive.

Dr. Levinson was an early promoter of the idea that companies, like people, had distinct personalities, or cultures, that grew out of their history and the demographics of their work force. He developed methods to identify and isolate the elements of a company's culture and discern their impact on workers. His 1972 book on the subject, ''Organizational Diagnosis,'' has been used widely as a business school text.

But as adept as Dr. Levinson was at diagnosing and curing corporate ills, his main focus was on preventing them. His forte was identifying and promoting the habits and attitudes that kept people functioning well, and beginning in 1968 he built a lucrative business around it through the Levinson Institute, a research and consulting concern in Jaffrey, N.H.

Dr. Ralph G. Hirschowitz, a psychiatrist and former colleague of Dr. Levinson's at the Harvard Medical School and later a faculty member at the institute, said, ''When it came to applying psychoanalytic principles to managing human beings, Harry was a true missionary.''

Harry Levinson was born on Jan. 16, 1922, in Port Jervis, N.Y. He was the oldest of three children of David Levinson, a tailor, and the former Gussie Nudell Levinson, both Jewish immigrants from Russia. His mother never learned to speak English, but she did complain loudly -- in Yiddish -- about the family's meager means, Dr. Levinson recalled.

''My teachers, not my parents, were the agents of my civilization,'' he told a reporter.

The young Harry learned early on that books could be a wonderful escape from family strife and poverty. For hours he would sit in the local public library, or huddled by the coal stove at home, and read book after book.

''That's what I remember vividly, Harry with his nose in a book,'' Elizabeth Mungoven, a friend of Dr. Levinson's since elementary school, said in 2005.

He loved writing. In seventh grade he won his first writing award, a silver medal (which he always kept) for an essay on President Franklin D. Roosevelt, who was then in his first term.

Harry's career goal as a teenager was to teach, but as a Jew in a time of virulent anti-Semitism, he believed his chances of landing a teaching job in New York State were slim. When a friendly high school guidance counselor persuaded him that he would do better in the Midwest, he enrolled in Kansas State Teachers College (now Emporia State University).

After receiving his bachelor of science degree in 1943, Dr. Levinson joined the wartime Army serving mostly in Italy, where he often tried to teach illiterate Army friends how to read. In 1946, he married his childhood sweetheart, Roberta Freiman, and then earned a master's degree from Emporia State and a doctorate in clinical psychology from the University of Kansas.

As part of his doctoral studies, Dr. Levinson spent two weeks observing the way mentally ill patients were treated at the Topeka State Hospital in Kansas, then submitted a paper describing how their treatment could be improved. His ideas fell on receptive ears; the hospital hired him. He then spent more than three years instituting better ways of keeping track of patients, treating their ailments and raising the hospital's profile with legislators and potential donors.