The efficacy of the 2 antimicrobial compounds, erythromycin and trimethoprim-sulphamethoxazole, were compared in the treatment of the clinical symptoms of cholera and the eradication of Vibrio cholerae O1 organisms from the stools of patients infected with tetracycline-resistant strains. 47 patients with a clinical diagnosis of cholera, without prior antibiotic therapy, were included in the trial and received either erythromycin, trimethoprim-sulphamethoxazole, or a placebo twice daily. The mean number of vibrios per gram of stool decreased from 5.2 x 10(8) +/- 0.3 per ml to 0 within 36 h of admission following either erythromycin or trimethoprim-sulphamethoxazole therapy, while organisms persisted in placebo-treated controls for more than 7 d. Clinically there was a significant reduction in the number of diarrhoeal stools per day and duration of diarrhoea in the erythromycin-treated group compared with the placebo-treated controls. During the study an isolate resistant to trimethoprim-sulphamethoxazole but sensitive to erythromycin was obtained. As an adjunct to oral rehydration therapy, erythromycin may serve as an effective alternative treatment for cholera, especially in areas where trimethoprim-sulphamethoxazole resistance may be emerging.