The oral single-dose-treatment of the acute gonorrhoeal urethritis of the male with 1.4 g pivampicillin and 1.0 g probenecid is one of the possible alternatives to a parenteral penicillin treatment. Experiments were performed on rabbits to determine if this dose of pivampicillin and probenecid could cure a simultaneously acquired syphilis at a very early stage of incubation. 300 treponems (Nichols strain, T. pallidum) were inoculated intratesticularly and 3 days later pivampicillin and probenecid were administered in doses which produced antibiotic serum levels similar to those in patients who had received a single oral dose of 1.4 g pivampicillin and 1.0 g probenecid. Controls over a 15-weeks period showed that this dosage did prevent the development of syphilitic orchitis and reactivity to the quantitative FTA-ABS-test. It is concluded that the treatment of acute gonorrhoea with 1.4 g pivampicillin and 1.0 g probenecid in general is sufficient to cure a simultaneously acquired syphilis.