We inoculated 45 female macaques in the cervix with Chlamydia trachomatis once weekly for 5 weeks and randomly assigned them to treatment with doxycycline (n=12), azithromycin (n=12), or placebo (n=21). At hysterectomy, cervical cultures remained positive in 12 of 21 placebo-treated monkeys, versus 0 of 12 doxycycline- or azithromycin-treated monkeys (P<.01); cervical ligase chain reaction remained positive in 15 placebo-, 1 doxycycline-, and 0 azithromycin-treated monkeys. Tubal swabs remained positive in 3 placebo-, 1 doxycycline-, and 0 azithromycin-treated monkeys. Immunopathologic damage was moderate to widespread in upper and lower reproductive-tract tissues from placebo- and doxycycline-treated monkeys but were significantly reduced in azithromycin-treated monkeys. Transforming growth factor- beta was also significantly less prevalent in azithromycin-treated monkeys. Azithromycin treatment dramatically reduced the inflammatory response and was highly effective in eradicating C. trachomatis from the lower and upper reproductive tract (12/12), compared with doxycycline (7/12) and placebo (3/21).