In 1969, he went to Dartmouth as a professor of geology.

Khan went to Michigan State University as a visiting professor in 1973 and remained there until 1979.

In 1969 he went to Temple University as a professor of pathology and was chairman of that department from 1974 to 1978.

In 1957 he went back to Texas as an assistant professor at the University of Texas.

Two years later he went to Tokyo Commercial University as a full professor.

That year he went to Michigan as an assistant professor of economics.

After retirement he went as a visiting professor to Harvard and then settled in Oxford.

In 1948 he went there for a short time as an honorary professor of economic history.

He first went to Harvard as an assistant professor in the late 1930's and returned in 1946 as a full professor.

Later he went back to Odense as a professor of bioinformatics.