A possible synergy has been shown between chemotherapy with praziquantel, PZQ (normally administered once in 12 months), and the immune system in mice infected with schistosomiasis. This has been supported by a reduction in the effectiveness of PZQ against adult schistosomes in T and B lymphocyte depleted mice. We have investigated the effect of a standard dose, 40 mg/kg, of PZQ on polymorphonucluecytes (PMN) spreading, granulocytes chemotaxis, adherence and lymphocyte blastogenic responses. Blood samples were collected from volunteer children with or without urinary schistosomiasis infection, after obtaining their consent. The results obtained showed that PZQ, three hours after administration (plasma half life; 1.5 h), appeared to significantly (p < 0.001) enhance the chemotactic affect of N-fmlp and the blastogenic effect of soluble schistosome egg antigen (SEA) and phytohaemaglutanin (PHA). It would be reasonable to conclude that these observed effects of PZQ may contribute to the overall mode of action of PZQ.