We examined effects of excimer laser irradiation on blood. Five vials, each of which contained 3ml of blood, were exposed to 37.5mJ laser beam at 10 PPS in repetition rate for 10, 20, 30, 40, 50 seconds. One vial was left untreated as a control. No change in hematocrit value was observed after excimer laser irradiation. In contrast, the level of plasma free hemoglobin rose progressively with each increased duration of exposure. This study indicates that the lysis of erythrocytes does not occur in the laser-exposed cells. However, the damage to erythrocyte membrane took place as it was evidenced by progressive hemoglobin leakage into plasma.