One hundred twenty-eight patients who had been treated for late latent syphilis were followed. Benzathine penicillin G (2.4 X 10(6) units given intramuscularly once a week for two weeks) was administered to 123 patients, and five patients were given tetracycline (500 mg orally four times daily for 12 days). Of these patients, 56 (44%) became seronegative within five years, and 72 (56%) had persistently positive reagin tests.