One hundred ninety-two female patients with acute urethral syndrome caused by Ureaplasma urealyticum were examined. First, patients were divided into two groups: those with clinical symptoms present for less than 3 weeks before the start of treatment and those with clinical symptoms 3 weeks or longer before the beginning of therapy. The patients were then further divided into groups and randomized to receive azithromycin once daily in a single dose of 1 g or 500 mg once daily for 6 days, or to receive doxycycline 100 mg b.i.d. for 14 days or 100 mg b.i.d. for 7 days (eight study groups in all). Clinical and bacteriological efficacy were evaluated 3 weeks after the end of therapy. In the group of patients with disease symptoms lasting for 3 weeks or longer, eradication and clinical cure rates were significantly higher after the administration of azithromycin at a dose of 1 x 500 mg/6 days than after a single dose of 1 g (p < 0.001).