PIP: A cross-sectional study was conducted in June-September 1991 in the oral rehydration unit of a children's hospital in Santo Domingo to determine the prevalence of enteric protozoa as a cause of diarrhea. The 100 randomly selected children were aged 3-35 months and had light to moderate dehydration and diarrhea of less than 15 days' duration. The relationship between the presence of protozoans and various risk factors was assessed following the model of a case control study, with children having protozoa infections considered cases and those with diarrhea but not protozoa infections considered controls. 79 of the children were under 1 year old. 36% were malnourished. 60% of the children's families had inadequate garbage disposal facilities, 23% lived in crowded conditions (defined as more than 3 persons per room), 10% drank nonpotable water, 7% lacked piped water, and 2% had no toilet facilities. 66% of the children were found to be positive for protozoa, with 26% positive for Giardia lamblia, 19% for Entamoeba histolytica, 17% for Cryptosporidium, 2% for Dientamoeba fragilis, and 2% for Isospora belli. 6 cases of mixed infection were observed. A significant relationship was found between infection and garbage disposal in the open air and between infection and ingestion of nonpotable water. The high prevalence of protozoa infection is consistent with recent clinical observations. Public health measures should be taken to improve sanitation and personal hygiene.