The purpose of this study was to determine the prevalence and to assess the efficacy of a single one gram oral dose of azithromycin under direct observed therapy of genital discharge due to Neisseria gonorrhoeae and Chlamydia trachomatis infections in STD clinic attenders in Trinidad and Tobago. All patients with genital discharge and their contacts were given one gram oral dose of azithromycin under direct supervision after collection of urethral and cervical swabs for N gonorrhoeae culture and smear and for C trachomatis antigen detection by ELISA. Clinical and microbiological evaluation was done on those who returned after 7-10 days for follow-up. Of the 735 patients who were enrolled in the study, 319 (43.4%) had N gonorrhoeae and 100 (13.6%) had C trachomatis. Only 151 (36%) of the 419 patients with a pathogenic isolate returned for clinical and microbiological assessment. The remaining 268 (64%) of the 419 patients were lost to follow-up. One hundred and forty-three patients (94.7%) had total abatement of signs and symptoms after taking azithromycin. One patient (0.65%), who had both N gonorrhoeae and C trachomatis, improved clinically with the drug. Seven patients (six with N gonorrhoeae and one with C trachomatis) failed to respond clinically to azithromycin. Microbiological eradication was achieved in 115 (100%) patients who had single infection with N gonorrhoeae and in 23 patients (96%) with C trachomatis infection. Of 12 patients with combined infections, N gonorrhoeae and C trachomatis were eradicated in 10 and 12 patients, respectively, after initial treatment. In two patients with combined infection, N gonorrhoeae continued to be isolated after treatment with azithromycin. A single one gram oral dose of azithromycin under direct supervision is useful in the treatment of uncomplicated genital infection with N gonorrhoeae and C trachomatis in STD clinic attenders in Trinidad.