Eighteen male patients with primary syphilis were randomly assigned to one of the following treatment schedules: ceftriaxone (3 g in a single intramuscular [im] injection), ceftriaxone (2 g im daily for two days), ceftriaxone (2 g im daily for five days), and benzathine penicillin (2.4 X 10(6) units in a single im injection). The single 3-g dose of ceftriaxone cured three men, one had a sustained response, and one failed to be cured. Of the patients given 2 g of ceftriaxone im daily for two days, three were cured and two had a sustained response. All three men treated with 2 g of ceftriaxone daily for five days had a sustained response. In the group given penicillin, three men were cured, one had a sustained response, and one was lost to follow-up.