There is some controversy regarding the effect of general inhalation anesthesia on platelet function. In 20 patients undergoing long operations over 3 hours, and anesthetized with either nitrous oxide-oxygen and enflurane (A group) or nitrous oxide-oxygen and halothane (B group), we could not find any clinically significant impairment of coagulation. Platelet functions were consecutively evaluated on the samples collected at preinduction, during anesthesia (3 hours) and at postoperation (24 hours) using an aggregometer and several aggregating agents including ADP, epinephrine, collagen and ristocetin. There were no statistically significant changes between the maximum aggregation rate of preinduction and that duirng anesthesia in either group.