The rate of a decreased response to ADP and a lack of response to epinephrine by platelets on the optical aggregometer is reported to be between 16% to 40% in studies on various populations. We aimed to evaluate the platelet functions and to determine the rate of lack of response to epinephrine in healthy young-adult men. A total of 52 healthy volunteers aged between 19 to 42 were evaluated. The subjects were classified into three groups as nonresponder, semiresponder and normal according to their response to 100 μM epinephrine on the optical aggregometer. The nonresponder rate was 7.7%, and the semiresponder rate was 5.8%. A decreased response to epinephrine was associated with both decreased maximum aggregation of ADP and collagen, and did not affect the aggregation of arachidonic asid and thrombin, and ATP release. In conclusion, impaired response to epinephrine may be seen in one in every 3-6 persons, and this impaired response may also affect the other stimulating agents. These properties may be protective against thrombosis since there is no bleeding tendency and have similarity to aspirin usage. © Gülhane Askeri Tip Akademisi 2006.