We performed a single blind controlled multicenter study in which we compared the efficacy and safety of 100 mg of doxycycline versus those of 1 g (3 x 10(6) IU) of spiramycin given orally twice daily for 14 days in the treatment of culture-positive Chlamydia trachomatis genitourinary tract infections. A total of 367 patients were enrolled in the study, and 364 patients were evaluable for safety and 265 patients were evaluable for efficacy. The cure rate between treatment groups was not statistically significant, being 98% (125 of 128 patients) in the spiramycin group and 100% (133 of 133 patients) in the doxycycline group. Female patients who received spiramycin were more likely to report dysethesias that resolved after the completion of therapy. The results of the study show that spiramycin is an effective drug for the treatment of C. trachomatis infection and warrants further assessment over a shorter treatment period (7 days) and during pregnancy.