The aetiology of acute diarrhoea was investigated in 245 children less than 3 years old in a paediatric outpatient clinic in southern India. In 55% of the children organisms were found in the stools, and one quarter were infected with multiple organisms. Viruses, enteropathogenic E. coli, shigella and campylobacter species accounted for 75% of all isolates. Cholera and helminthiasis were rare, and no child had amoebiasis. Clinical findings were useful in the diagnosis of shigella and rotavirus infection only. Children with shigellosis had classical dysentery, and a greater number of stools; they were unlikely to be breast-fed, to be less than 6 months old, or to have watery stools. Rotavirus infections were characterized by vomiting. Only 20% of the 245 children had an infection which could be treated effectively with antimicrobials.