Through the use of portable ultrasonography, eight cases (2%) of periportal fibrosis were identified in a random sample of 400 subjects selected from a village with a high prevalence and morbidity due to schistosomiasis haematobium in the White Nile Province of Sudan. In contrast, 36 cases (15%) of fibrosis were seen in an area with a similar prevalence and morbidity due to schistosomiasis mansoni in the Gezira Managil region of Sudan. Although there was only one case of Schistosoma mansoni as determined by repeated stool examination of the entire sample population in the first village, the majority of those with fibrosis and age-matched controls showed serologic evidence of active S. mansoni infection. This led to the conclusion that the cases of periportal fibrosis seen in the White Nile Province are most probably due to S. mansoni rather than to S. haematobium.