Dr. Eugene Meyer III, 66, a professor-emeritus in medicine and psychiatry at the Johns Hopkins University School of Medicine and a member of the board of directors of The Washington Post Co., died yesterday at his home in Washington. He had cancer.

Dr. Meyer was the son of Eugene Meyer, the late publisher of The Washington Post. He was born in New York City. He was educated at Yale University, where he graduated in 1937, and at Johns Hopkins, where he earned a medical degree in 1941.

He began his career in medicine as an internist. Having become fully trained in that discipline, he undertook the study of psychiatry. His professional reputation stands on the importance he accorded to the interaction between emotional and organic disorders.

Colleagues at Johns Hopkins credit Dr. Meyer with pioneering work in studying the emotional dimension of physical illness. Partly because of his work, they said, this field has become a focal point of many federal programs providing psychiatric care.

According to Dr. Victor McKusick, the chairman of the department of medicine at Johns Hopkins, Dr. Meyer may have become interested in bridging the gap between psychiatry and medicine while serving in the Army Air Forces in World War II. After being stationed in the Mediterranean, he was assigned to a military convalescent hospital in St. Petersburg, Fla., as a neuropsychiatrist. He observed that many of the patients had emotional as well as physical problems.

In any case, he completed residencies in medicine at the Peter Bent Brigham Hospital in Boston and at Johns Hopkins. Then, from 1947 to 1949, he studied psychiatry at the Henry Phipps Psychiatric Clinic at Johns Hopkins. He joined the faculty of the medical school as an instructor in 1949 and in 1951 established the Psychiatric Liaison Service at the medical school. The purpose of the service, which Dr. Meyer headed until he retired and became a professor emeritus in 1980, was to care for the psychiatric as well as the physical needs of patients.

Dr. Meyer was "one of the pioneers in investigating the interface of psychiatry and internal medicine," Dr. McKusick said.

"What he did was a very special sort of bed-side teaching, a conference about a patient and a patient's problems, both medical and emotional," said Dr. Richard S. Ross, dean of the Johns Hopkins medical school.

"Prior to his program the interest of psychiatrists in medical patients was minimal," said Dr. Paul McHugh, the director of the department of psychiatry at Johns Hopkins. "We concentrated only on behavioral problems, not upon the suffering and complications that patients experience as a result of medical and surgical disease. Since that time, consultation and liaison psychiatry have become a dominant force."

An important aspect of Dr. Meyer's work was his insistence that physicians recognize that physical disorders can cause psychological ones, just as psychological ills can cause physical ones. Medicine now regards it as a truism, for example, that ulcers may cause psychological disorders, and vice versa.

Beyond his role in helping to draw medicine and psychiatry together, Dr. Meyer was regarded as a skillful teacher.

"Dr. Meyer made that which can be so vague concrete, teachable and accessible to doctors," Dr. McHugh said.

Dr. Meyer became a full professor of psychiatry in 1966 and a full professor of medicine in 1970. He continued to teach until shortly before his death.

As a businessman, he was a major stockholder of The Washington Post Co. He served on its board of directors for many years.

His marriage to Mary Bradley Meyer ended in divorce.

Survivors include a son, Eugene Bradley Meyer, of Lincoln, Mass.; three daughters, Ruth Meyer Guffee of West Haven, Conn., Anne Meyer of Wenham, Mass., and Elizabeth Ernst Meyer of Edgartown and Cambridge, Mass.; three sisters, Katharine Graham, the chairman of The Washington Post Co., of Washington, Mrs. Pare Lorentz of Armonk, N.Y., and Ruth Meyer Epstein of Scarsdale, N.Y., and five grandchildren.