A method for inhibiting blood platelet aggregation in humans, and promoting vasodilation in humans, by administering to a human in need of the same an effective amount of 2-hydroxy-3-isopropyl-5,6-dimethylpyrazine or a hydrate or a pharmaceutically acceptable non-toxic salt thereof. Administration can be orally in an amount of about 0.02-12 mg/kg body weight per day, or parenterally in an amount of about 0.01-6 mg/kg of body weight per day.