Ciprofloxacin was evaluated in chlamydial infections of the urogenital tracts of women treated with a dosage regimen of 500 mg orally twice a day for seven days. Of the 40 women evaluated, 30 were infected with Chlamydia trachomatis only, two were infected with Neisseria gonorrhoeae only, and a further eight had combined gonococcal and chlamydial infections. Ten were found to be harbouring Chlamydia trachomatis in the urethra as well as the cervix. Neisseria gonorrhoeae was eradicated from all patients with or without concomitant chlamydial infection. The overall chlamydial reisolation rates were 14% (5/35) four weeks after treatment and 23% (6/26) 11 weeks after treatment. The organism was not reisolated from the urethra of any of the patients after treatment. Ciprofloxacin was effective against Mycoplasma hominis, but almost completely ineffective against Ureaplasma urealyticum.