Abstract: The inhibiting action of chlorpromazine and reserpine on the emetic effects of apomorphine, α-dichroine, the strongly basic portion of Hydrangea macropkylla f. hortensia wilson alkaloids and ammonium antimonyl gluconate was investigated in dogs. Previous administration of chlorpromazine increased the threshold emetic dose of apomorphine 6—12 times, that of the strongly basic portion of the Hydrangea macrophylla alkaloids 0.5—2.0 times and only slightly increased that of α-dichroine. Reserpine showed no or very little inhibiting action on the emetic effect of α-dichroine. Previous administration of neither chlorpromazine nor reserpine changed the threshold emetic dose of orally administered ammonium antimonyl gluconate. The use of chlorpromazine seemed to delay the onset of emesis caused by ammonium antimonyl gluconate.