Low concentrations of staphylotoxin hemolyzed human erythrocytes at 37 degrees following the kinetics of the first order, high concentrations--by means of kinetics of the second order. Effect of the toxin was distinctly augmented with increase of temperature above 20 degrees. Treatment of erythrocytes with proteolytic enzymes elevated the cell sensitivity to the staphylotoxin. Liposomes, containing a mixture of lecithin, cholesterol and/or hydrocortisone as well as the total lipid fraction from bovine brain, did not affect the hemolysis, but the liposomes containing lecithin and phosphatidyl serine augmented the staphylotoxin effect. The phenomenon found might occur due to enriching of erythrocyte membranes with phosphatidyl serine.