Between March and July, 1987, faecal specimens from 371 diarrhoeal children reporting to four hospitals in the district of Kurunegala, Sri Lanka and from 121 controls with other diseases were investigated for enteric pathogens. All specimens were tested for Shigella spp, Salmonella spp and enteropathogenic Escherichia coli (EPEC). In addition, parasitic pathogens, heat labile enterotoxigenic Escherichia coli (ETEC LT), Campylobacter and rotavirus were sought among subsamples of the cases and controls. One or more pathogens were detected in the faecal specimens of 53.7% of the diarrhoeal children and 19.6% of the controls (P less than 0.001). Rotavirus was the most frequently identified pathogen. Cases (21.9%) were more likely to be positive for rotavirus than controls (6.5%) (p less than 0.05). Among children with diarrhoea the peak prevalence of rotavirus occurred in the 6-11 months age group. Shigella spp were the second most frequently isolated pathogens and the single most common cause of diarrhoea in children over two years of age. Again, cases (16.4%) were more likely to be infected than controls (1.7%) (p less than 0.001). Salmonella spp were isolated from 7.5% of diarrhoeal children and 3.3% of the controls (p greater than 0.10). Other pathogens had prevalence rates of less than 5%. Vomiting was associated with rotavirus diarrhoea (p less than 0.001), and fever with shigellosis (p = 0.02). In view of the different transmission routes and characteristics of the most important pathogens detected in this study it appears unlikely that a single environmental intervention can solve the public health problem posed by diarrhoeal diseases in Sri Lanka.