Objective: To compare the efficacy and safety of a 7-day course of treatment with oral grepafloxacin, 400 mg once daily, and oral doxycycline, 100 mg twice daily, in patients with chlamydial cervicitis. Methods: Women aged 18 years or older attending 17 sexually transmitted disease clinics in the United States who had clinical signs of mucopurulent cervicitis or who had a recent positive culture or nonculture test for Chlamydia trachomatis or who had contact with a male partner with a positive culture for C. trachomatis were enrolled into this randomized, double-blind, active- controlled clinical study. The diagnosis of chlamydial cervicitis was based on culture for C. trachomatis. Patients were randomized to receive a 7-day course of treatment with either oral grepafloxacin, 400 mg once daily, or oral doxycycline, 100 mg twice daily. Response to therapy was assessed 3-8 days and 21-28 days after completion of treatment. The primary measure of efficacy was eradication of C. trachomatis at the 21-28 day follow-up visit. Clinical success, defined as improvement or complete resolution of the signs and symptoms of cervicitis, was a secondary measure of efficacy. Results: Of the 451 female patients enrolled, 228 received grepafloxacin and 223 received doxycycline. In all, 154/451 (35%) patients were evaluable at the 21-28 day follow-up (81 who received grepafloxacin and 73 who received doxycycline). Microbiologic and clinical success rates demonstrated the equivalence of the two treatments. The C. trachomatis eradication rates were 96.3% (78/81) and 98.6% (72/73) for patients receiving grepafloxacin or doxycycline, respectively. The two study drugs were also equivalent in resolving clinical signs and symptoms, with clinical success rates of 88.9% (64/72) and 89.5% (51/57) for patients treated with grepafloxacin and doxycycline, respectively. Both drugs were well tolerated, with 47% of patients receiving grepafloxacin and 46% of patients receiving doxycycline experiencing drug- related adverse events, none of which was serious. Conclusions: Seven days of treatment with oral grepafloxacin, 400 mg once daily, was as effective as 7 days of treatment with oral doxycycline, 100 mg twice daily, in patients with cervicitis caused by C. trachomatis. Both agents were well tolerated and had comparable safety profiles. Grepafloxacin's once-daily dosing regimen may offer advantages in terms of patient compliance.