The objective of the study was to determine the prevalence of parasitic infestations in children with diarrhoea and its effect on the course of the diarrhoea. A case control study was carried out at the Lady Ridgeway Hospital, Colombo, Sri Lanka. The study population consisted of 940 children with acute diarrhoea and 260 children admitted for conditions other than diarrhoea. The first sample of stool was examined for bacteria (Sal monella spp, Shigella spp, Aeromonas spp, Campylobacter spp, Vibrio cholerae, Vibrio parahaemolyticus and Enteropathogenic E.coli), viruses (rotavirus and adenoviruses) and parasites (En tamoeba histolytica, Cryptosporidium spp, Giardia lamblia, Ascaris lumbricoides, Trichuris trichiura, Necator americanus and Enterobius vermicularis) us ing standard techniques. Among children with diarrhoea, 9.3% had parasitic infections and 6.5% were infected with parasites which are known to cause diarrhoea. In 4.5%, the parasite was the only pathogen that was detected. Malnutrition was found to-be more prevalent in children whose diarrhoeal illness was associated with parasites especially in children who had G. lamblia and T.trichiura infections. When Salmonella and rotavirus diarrhoea was associated with nondiarrhoeal' parasitic agents more severe symp toms were observed and the duration of the ill ness was prolonged in rotavirus diarrhoea. The results show that parasites may alter the course of acute diarrhoea due to bacteria and vi ruses. Therefore parasitological investigations should complement bacterial and viral diagnosis in patients with diarrhoea as specific therapy could be instituted.

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