Twenty-five male patients with nongonococcal urethritis including 15 chlamydial infections were treated with spiramycin for ten days. All but four patients had been treated previously, mostly with tetracyclines. Chlamydia trachomatis was cultured in seven patients and was detected in three additional men by immunofluorescent smear. Five other patients had antibodies to chlamydia, and one patient yielded a positive culture for Ureaplasma urealyticum and Mycoplasma hominis. A succussful clinical response was observed in 64% of the patients; C. trachomatis was eradicated from six of seven patients with positive cultures and the three positive direct smears were negative after treatment. It is concluded that spiramycin can be used effectively for the therapy of acute nongonococcal urethritis, as well as in patients who have failed to respond to previous treatment with tetracyclines and erythromycin.