Two hundred and eighteen residents (131 healthy and 87 mentally or physically retarded) of a children's nursery, a foster house and a rehabilitation centre for the handicapped in Abha, southwestern Saudi Arabia, were examined for intestinal parasitism. About 30% of the population of the three communities were found to harbour asymptomatic infections with either Giardia lamblia and/or Entamoeba spp. Giardia cysts were identified in 19.3% of those examined. Entamoeba histolytica was found in 18.4% of the residents of the rehabilitation centre only. Entamoeba coli infections were found in residents of both the foster house and rehabilitation centre (6.0 and 25.3% respectively). The prevalence of infection with the three parasites was significantly higher in the rehabilitation centre than in the children's nursery and foster house.