Background: Penicillin is the only medication currently recommended for treatment of early syphilis in non-penicillin-allergic patients. Preliminary data suggest that azithromycin may be effective for syphilis therapy. Study Design: This was a randomized, comparative pilot study of intramuscular injections of benzathine penicillin G and two oral azithromycin regimens for treatment of syphilis. Methods: We randomly assigned patients with early syphilis to treatment with either intramuscular injections of 2.4 million units of benzathine penicillin G or azithromycin administered orally, either as a single 2.0-g dose or as two 2.0-g doses given 1 week apart. Serological response to therapy was evaluated at 3, 6, 9, and 12 months following therapy. Participants whose rapid plasma reagin (RPR) test became nonreactive or whose RPR titer decreased ≥2 dilutions were classified as responding to therapy. When serological tests did not show a response to therapy, the treatment was classified as a failure if RPR titers increased ≥2 dilutions. Nonresponders were those whose serologic titers remained within ±1 dilution of the initial RPR titer. Results: Cumulative response rates were as follows: benzathine penicillin G, 86% (12 of 14); azithromycin, 2.0-g single dose, 94% (16 of 17); and azithromycin, two 2.0-g doses given 1 week apart, 83% (24 of 29). Therapy failed for one patient treated with benzathine penicillin and one patient treated with the two-dose azithromycin regimen, whereas in six patients the clinical manifestations of infection resolved but there was no serological response. Conclusion: Oral therapy with 2.0 g of azithromycin as a single dose or as two doses 1 week apart is a promising alternative to therapy with benzathine penicillin G for syphilis and should be studied further.