Following demonstration of in vitro activity of amoxycillin against Treponema pallidum, a clinical research group was set up to study the effects of amoxycillin against various stages of syphilitic infection in men. A total of eighty-nine cases, fifteen primary, twenty-nine secondary, thirty late and fifteen adult congenital patients have been investigated. One hundred per cent effectiveness was recorded for primary and secondary syphilis; 66.7% for late syphilis and 60% success for adult congenital syphilis. In 10.4% of cases there was a transient elevation of SGOT and SGPT although it is not certain whether this was a reaction to the drug itself. There were three incidences of drug-related rash and two other minor side-effects. Amoxycillin is thus a safe and effective oral agent for the treatment of all stages of syphilis in man.