During the spring peak of diarrhoea in Bangladesh, 113 consecutive patients who represented a systematic 4% sample of all patients attending an urban diarrhoea treatment facility between 18 and 23 April 1995 were studied. The study was conducted to characterize enteric pathogens associated with the spring peak of the diarrhoea outbreak in Bangladesh and to describe clinical and epidemiological features of the patients. The spring peak is traditionally thought to be mostly due to V. cholerae O1. However, the most common cause of diarrhoea among the study patients was enterotoxigenic Escherichia coli (36%) followed by Vibrio cholerae O1 (23%). The V. cholerae O1 patients attended significantly (p < 0.01) sooner after onset of diarrhoea than enterotoxigenic E. coli (ETEC) patients. Studies of behavioural and environmental characteristics are important to determine risk factors for observed higher proportion of ETEC infection during seasonal diarrhoea peaks.