Abstract: Using Clark oxygen electrode, the normal rate of respiration of Schistosoma japonicum were determined in vitro. The rate of respiration of adult schistosomes was found to be 1.47+0.19 nmol O2/pair of worm/min or 6.89+1.13 nmol O₂/mg dry wt/min. It was 2.5 fold higher than that obtained by manometric method. This indicates that S. japonicum did have an active aerobic metabolism. Both in vitro and in vivo experiments showed that potassium antimony tartrate inhibited markedly the respiration of the worms, whereas the rate of glycolysis was affected only slightly. Our results seemed to be inconsistent with those suggested by Bueding who had attributed the mode of action of antimonial drugs to the inhibition of phosphofructokinase.Diamide, a well-known specific sulfhydryl agent, was shown to inhibit similarly the respiration of schistosomes. This led us to assume that antimonial drugs might act on important enzyme systems containing SH-groups.Pyquiton was similar to local anesthetics (lidocaine and bupivacaine) in that they stimulated the respiration of worms in vitro. It is interesting to note that all these compounds have a glycinamide structure (Fig 1). Thus, it appears that the mode of action of pyquiton may be related to that of local anesthetics, acting on worm tegument and influencing the permeability of cations.Pyquiton did show a slight effect on the glycolysis of schistosomes. But the ratio of the amount of lactic acid formed to that of the combined consumption of glycogen and glucose remained to be 1.