Lipophilic Fraction (LF) from Panax ginseng C.A. Meyer strongly inhibited human platelet aggregations induced by thrombin. When platelets were prelabeled with 5-hydroxy[G-$^3$H]-tryptamine (serotonin) and then stimulated by thrombin, LF inhibited the release of serotonin in a dose-dependent manner. From this result, we suggest that LF have antiplatelet and antimigraine functions by inhibiting the release of serotonin.