Serological indicators for disease activity and portal vein obstruction and/or deviation were assessed in 23 patients with hepatosplenic schistosomiasis before, and up to 18 months after, praziquantel treatment, as well as in 25 matched local controls. Cessation of egg-induced immunopathology was reflected by the return to normal of serum procollagen-III-propeptide and neopterin concentrations. Reversibility of portal vein pathology was indicated by normal clearance of cholylglycine in cases without signs of decompensating portal hypertension. In most patients with a history of ascites and/or haemorrhage, serum cholylglycine concentration remained pathological. The results provide evidence that the fibrogenic process ceases after specific chemotherapy, and that portal vein pathology regresses in a substantial proportion of hepatosplenic schistosomiasis cases.