Seventeen aporphines were tested for antiplatelet activity. L-(+)-hemovine HCl and 7-hydroxydehydrothalicsimidine strongly inhibited platelet aggregation induced by adenosine 5'-diphosphate (ADP), arachidonic acid (AA), collagen, and platelet-activating factor (PAF). The latter showed the strongest antiplatelet activity with an IC50 of 70.4 microM against AA-induced platelet aggregation.