To compare the clinical and microbiological efficacy of azithromycin in curing chlamydial infections in women with that of lymecycline, and with a view of the possibility of minimizing the problem of compliance by means of single-dose administration, 146 women with culture-positive Chlamydia trachomatis infections were randomly assigned to treatment with a 1 g bolus dose of azithromycin or a 10-day course of lymecycline 300 mg twice daily. Clinical and microbiological evaluations were performed and adverse effects monitored at check-ups after 15-35 and 40-65 days. Of the 146 patients enrolled in the study, 120 were evaluable. At the second check-up, C. trachomatis was found to have been eradicated in all patients in both treatment groups. Of the 51 patients who had clinical signs and symptoms of genital infection at enrolment, 96% (22/23) of those in the azithromycin group were considered cured (n = 18) or improved (n = 4), as compared with 100% (28/28) of those considered cured (n = 22) or improved (n = 6) in the lymecycline group. Adverse events related, or possibly related, to treatment were reported by 16 (21.6%) of the lymecycline group, but by only 6 (8.3%) of the azithromycin group. The 2 drugs were comparable with regard to microbiological and clinical efficacy in the treatment of genital chlamydial infection in women. The markedly lower rate of side-effects associated with azithromycin may be a feature conducive to patient compliance.