Hemolysis of erythrocytes was induced after addition of ethanol solution of photooxidized psoralen, while the substance irradiated in absence of oxygen did not cause the cells hemolysis. The rate of hemolysis correlated with concentration of photooxidized psoralen in a sigmoid type. Similar concentration-dependent effect has been known for digitonin. Digitonin elevated the ionic permeability of lecithin-cholesterol liposomes but did not affect the permeability of lecithin liposomes. Photooxidized psoralen did not effect apparently on liposomes of both types. These data suggest that hemolytic effect of photooxidized psoralen did not relate to the substance interaction with cholesterol.