An open randomised controlled clinical trial with 160 adults with acute watery diarrhoea and severe dehydration compared the efficacy of varying regimens of norfloxacin and doxycycline for the treatment of cholera caused by Vibrio cholerae 0139 Bengal. Data were analysed for the 111 patients who were faeces culture positive for V. cholerae 0139. In addition to rehydration therapy, 28 patients received 300 mg of doxycycline as a single dose on admission, 26 patients received norfloxacin 400 mg bd for three days, 28 patients received a single dose of 800 mg of norfloxacin and 29 patients received no antibiotic (control group). Patients in the three treatment groups and control group had comparable characteristics on admission. All three treatment groups had reduced stool output, duration of diarrhoea and fluid intake compared with the control group. Multidose norfloxacin treatment significantly reduced stool output, duration of diarrhoea and fluid requirement compared with the other regimens.