In 1966, Acar became head of the Department of Medical Microbiology and Infectious Diseases at the Hôpital Saint-Joseph in Paris, staying there until 1999. At the same time, he was head of Medical Microbiology at the Hôpital Broussais. He was a professor of medical microbiology at Pierre and Marie Curie University from 1973 until 1980, and was head of that department from 1980 to 2000.