Inocula of S. mansoni and T. gondii well tolerated by albino mice when given singly, were given concomitantly to groups of animals. Few notable effects were observed when toxoplasmosis preceded schistosomiasis, but the S. mansoni leads to T. gondii model, with an interval of 59 days between infections, led to massive mortality, great weight loss and a striking splenomegaly. These findings are very similar to data from previous work on the S. mansoni leads to Trypanosoma cruzi model. The authors believe that other examples of such a type of potentialization should be searched for in human schistosomiasis also.