Faecal samples from 150 buffalo calves, one to 150 days old, located in various districts of Sri Lanka, were examined for group A rotavirus antigen by a screening enzyme linked immunosorbent assay (ELISA). Positive samples were confirmed by the blocking ELISA. In the calves studied 27.3 per cent were diarrhoeic, and the rest were non-diarrhoeic but were in contact with the animals showing diarrhoea. Antigen was detected in 36.6 per cent of the diarrhoeic animals and in 11.9 per cent of the non-diarrhoeic animals. There was a strong association between the presence of antigen in faeces and diarrhoea in these animals (chi 2 = 46.98; P < 0.001). Of the 146 serum samples examined for antirotaviral antibodies, by the blocking ELISA at a single serum dilution (1:20) against a constant dose of antigen (8 units), 68.5 per cent were positive indicating a widespread infection with the virus in the population studied. This is the first record of the detection of rotavirus and its association with diarrhoea in buffalo calves in Sri Lanka.