Ultrasonography was used in a village in the Gezira-Managil scheme in the Sudan to identify patients with Symmers' fibrosis. In a random sample from patients with active Schistosoma mansoni infection, 238 patients were found to have no liver involvement while 59 had Symmers' periportal fibrosis. Patients were treated with a single dose of 40 mg/kg body weight of praziquantel. Six months after dosing, 51% and 58% were cured of the infection with 81% and 84% reduction in egg burden in the Symmers' and non-Symmers' patients, respectively. The drug was equally well tolerated by the two groups. It is concluded that patients with Symmers' fibrosis respond to praziquantel and tolerate the drug in a similar manner to patients without Symmers'.