Prealbumin, prekallikrein and prothrombin were evaluated in 20 patients with the hepatosplenic form of schistosomiasis and in 18 subjects of a control group. With the prealbumin concentration values obtained in the latter group a reference interval (0.5 — 99.5%) of 97 to 389 mg/L was calculated and plasma levels below 97 mg/L assessed in 2 patients a deficiency in hepatic synthetic capacity. Mean (± SEM) prealbumin concentration in the 18 remaining patients (232 ± 13 mg/L) did not differ (p > 0.05) from that of the control group (243 ± 11 mg/L). Otherwise these 18 patients had both mean plasma prekallikrein (34 ± 1.3 /μKat/L) and prothrombin-antigen (81 ± 3 mg/L) concentrations lower (p < 0.01) than those of the control group (40 ± 1.4 μKat/L and 100 ± 3 mg/L, respectively). The present findings do not necessarily rule out the possibility that prekallikrein and prothrombin may asses a minimal hepatocellular damage earlier than prealbumin; but, since the latter protein have a shorter half-life than the formers and is a reliable index of hepatic synthetic capacity, the present report supports the hypothesis of an increased turnover of clotting proteins in some patients with the hepatosplenic form of schistosomiasis.