In a controlled trial of the effects of oral antibiotics in treating cholera in children in Dacca, East Pakistan, tetracycline was the most effective of 4 antibiotics tested in reducing stool volume, intravenous fluid requirement, and the duration of diarrhoea and positive stool culture. Increasing the duration of tetracycline therapy from 2 to 4 days, or increasing the total dose administered, resulted in shorter duration of positive culture, but did not affect stool volume or duration of diarrhoea. Only 1% of the children receiving tetracycline had diarrhoea for more than 4 days. Tetracycline was significantly more effective than intravenous fluid therapy alone, regardless of severity of disease.Chloramphenicol, while also effective, was inferior to tetracycline. Streptomycin and paromomycin exerted little or no effect on the course of illness or duration of positive culture. Therapeutic failures with these drugs were not due to the development of bacterial resistance.From these findings, tetracycline appears to be the drug of choice against Vibrio cholerae infection in children. Oral therapy for 48 hours is effective clinically, but is associated with 20% bacteriological relapses when the drug is discontinued; it is not known whether extending the therapy for a week or more would eliminate such relapses.