A model of acute schistosomiasis of the mouse was used to observe whether curative treatment would be followed by an enhancement of the hepatic and splenic lesions, as a consequence of the massive destruction of worms and eggs within the portal system. Mice infected with 50 cercariae of Schistosoma mansoni were treated with both oxamniquine and praziquantel on the 50th day of infection and submitted to a sequential histologic examination from the 2nd to the 45th day after treatment. Although severe focal lesions due to dead and disintegrating worms were present in the livers of the treated animals, no aggravation of the general changes (reactive hepatitis and splenitis, or periovular granulomas) was seen in comparison with a control non-treated group. Of 50 animals treated during the acute phase of schistosomiasis only one died spontaneously, while 16 out of 30 infected controls died before the end of the experiment. The present investigation indicates that curative treatment during the acute phase of schistosomiasis does not enhance previous lesions at first and results in progressive disappearance of the lesions starting six days following chemotherapy.