2300 persons from 25 communities in Harerge Administrative Region were examined for intestinal helminths. The overall prevalence rates were: Schistosoma mansoni 19.4%, Ascaris lumbricoides 13.4%, Trichuris trichiura 7.9%, and Taenia species 5.8%. Other parasites found in less than 3% included: Hymenolepis nana, Hymenolepis diminuta, Enterobius vermicularis, Strongyloides stercoralis and hookworms. Three age groups, 5-9, 10-14, and 15-19 years, had approximately similar prevalence (34.9-38.8%), but younger children had heavier egg loads (geometric mean egg output per gram of feces (EPG) of 347, 340 and 248, respectively). Boys had a higher prevalence of egg load than girls (42.4%, 395 EPG vs 26.5%, 277 EPG). Infection rates among Moslems were higher than Christians (45.5 vs 23.7%), but they had smaller egg output (333 vs 412 EPG). The frequency of light, moderate and heavy infections showed a normal distribution at 27, 46 and 27%. Biomphalaria pfeifferi was found to be infected with S. mansoni in Hirna (42/250), Esakly (6/80) and Genda Adem (20/200), the latter two in the Erer valley. Urine samples from 8 localities were negative for S. haematobium infection. The need for further study in several river valleys with agricultural potential is suggested.