Recently, there have been many cases in which nitroglycerin (TNG) is used for anesthesia for patients with low blood pressure. Since, it has been reported that TNG suppresses the platelet aggregation function in vitro. Verapamil (Vp), known as another platelet aggregation suppressant, and nicardipine (Nc) were used together with TNG and the platelet aggregation function was studied in vitro and in vivo. The results of the in vitro experiment showed that TNG 250 ng.ml-1 + Vp 250 ng.ml-1 suppressed the platelet aggregation function, and when TNG + Vp (was used for low hypotensive anesthesia, a large amount of Vp i.e. over 15 mg of Vp is injected as a bolus into the artery, there is a possibility the platelet aggregation function will be suppressed. No platelet aggregation function suppression was found when TNG+Nc was used in hypotensive anesthesia.