Praziquantel, (+)- is the dextrorotated (+) isomer of Praziquantel. Praziquantel (PZQ) is the drug of choice against schistosomiasis. Since exposure of schistosomes to the drug is associated with calcium influx and muscular contraction, calcium channels have been suggested as the target. It is a specific pharmacological effect seen exclusively with the active levo-R(-)stereo isomer of the drug. Praziquantel, (+)- apparently contributes little to the therapeutic efficacy of Praziquantel. In vivo, single 400-mg/kg oral doses of Praziquantel, (-)- and Praziquantel, (+)- achieved worm burden reductions of 100 and 19%, respectively. Moreover, worms treated in vivo with Praziquantel, (+)- displayed an only transient hepatic shift and returned to the mesenteric veins within 24 h.