We recently identified sodium n-propyl thiosulfate (NPTS) and sodium 2-propenyl thiosulfate (2PTS) from boiled onion and garlic, respectively, as causative agents of hemolytic anemia in dogs. We present here data concerning the effects of these alk(en)yl thiosulfates on superoxide (O(2)(-)) generation in peripheral polymorphonuclear leukocytes (PMNs) and on adenosine 5'-diphosphate (ADP)-induced platelet aggregation in dogs and humans in vitro. Both NPTS and 2PTS increased O(2)(-) generation significantly (P<0.05 at 1mM NPTS, P<0.005 at 0.1 and 1mM 2PTS) and reduced its reaction time significantly (P<0.05 between 0.01 and 1mM NPTS and at 1mM 2PTS) in canine PMNs stimulated by phorbol 12-myristate 13-acetate, compared with the control without alk(en)yl thiosulfates. However, a tendency to return to the control level was observed at 10mM of the alk(en)yl thiosulfates in both O(2)(-) generation and its reaction time. Although NPTS and 2PTS did not exert any significant effect on the O(2)(-) generation in human PMNs, 2PTS reduced its reaction time significantly (P<0.05) at 1 and 10mM compared with the control, showing that 2PTS accelerated O(2)(-) generation in human PMNs. The difference in effects on O(2)(-) generation may be due to that in susceptibility to alk(en)yl thiosulfates between canine and human PMNs. On the other hand, NPTS and 2PTS were shown to significantly inhibit ADP-induced platelet aggregation at 0.01mM (P<0.01) in canine platelets and at 0.001-0.1mM (P<0.05) in human platelets. In contrast, the maximal aggregation percentage returned to the control level at 1mM of alk(en)yl thiosulfates in both canine and human platelets. From these results, we conclude that NPTS and 2PTS have the potential to promote immune functions and prevent cardiovascular diseases.