The macrolide antibiotic rosaramicin inhibits in vitro growth of Chlamydia trachomatis. Rosaramicin (1 g daily given to 18 patients for seven days) and erythromycin stearate (2 g daily given to 19 patients for seven days) were compared in the treatment of chlamydial cervicitis. Cultures of cervical specimens obtained nine to 11 days and 24-32 days after commencement of therapy were negative for all rosaramicin-treated patients seen at follow-up. The first follow-up culture of one erythromycin recipient was positive. The extent of cervicitis decreased in all patients after treatment, but the only patients to achieve a completely normal cervical appearance were those with minimal-to-moderate lesions before treatment. Gastrointestinal side effects, including nausea, vomiting, and abdominal pain, occurred in ten of 19 patients given erythromycin and in 13 of 18 given rosaramicin. Minimally elevated levels of alanine aminotransferase in serum occurred in four (22.2%) of 18 rosaramicin recipients. It is concluded that rosaramicin and erythromycin stearate both eradicate C. trachomatis cervical infection but frequently cause adverse gastrointestinal effects.