During studies on schistosomiasis in the Yemen Arab Republic, 1,302 urine and 397 stool samples from inhabitants of various areas (mostly rural) were examined, and 137 water bodies were searched for snails. Results indicate the occurrence in most localities of both urinary and intestinal schistosomiasis, with a patchy distribution and various infection rates. The highest prevalence of Schistosoma haematobium infection, reaching 100%, was found in villages in the south. Snail intermediate hosts of both schistosomes were found in many habitats in 5 of the 6 provinces visited, and experimental studies showed Bulinus truncatus and Biomphalaria pfeifferi to be susceptible to infection with Schistosoma haematobium and S. mansoni, respectively. It is estimated that more than one million people in Yemen may be infected with one or both of these schistosomes.