A survey for transmission of schistosomiasis was carried out in one of the labour villages of Wonji Sugar Estate, Ethiopia. Little or no schistosomiasis was present prior to establishment of this irrigation scheme. The survey revealed that 82% of the children between 5-14 years were now excreting S. mansoni eggs, and high intensities of egg excretion were observed (geometric mean intensity 377 eggs/g faeces, with 26% excreting greater than or equal to 1000 eggs/g). Large numbers of Biomphalaria pfeifferi snails were discovered in the irrigation canals near the village, of which 5% were shedding schistosome cercariae. No cases of urinary schistosomiasis were seen, although intermediate hosts of this infection were present. Poor maintenance of sanitary and water supply facilities, combined with a lack of community involvement in the control measures, were identified as major contributors to the dramatic rise in transmission. All children infected with S. mansoni were treated with praziquantel (40 mg/kg body weight). A follow up one month after chemotherapy indicated a cure rate of 69% and a reduction in geometric mean egg output of 77%.