Homosexual relations play an important part in the transmission of infectious syphilis. A preponderance of the males with infectious syphilis treated in Los Angeles City Health Department clinics in 1959 admitted to exclusively homosexual relations during the period in which they became infected. In the interviewing of males with infectious syphilis, inquiry should routinely be made relative to possible homosexual relations, for investigation of the sexual partners of homosexual males is particularly productive in terms of new case finding. The practicing physician's awareness of the epidemiological significance of homosexual activity will influence his degree of clinical suspicion, his attitude in the physician-patient relationship and his concept of the opportunity and responsibility of bringing to examination the infected patient's sexual partners.