1. The hemolysis by serratamic acid, "N-(D-3-hydroxydecanoyl)-L-serine and N-(D-3-hydroxydodecanoyl)-L-serine", was investigated with human and animal erythrocytes using serratamic acid-containing liposomes. 2. The hemolytic activity was found to depend on the incubation temperature and the concentration of the liposomes. 3. The concentration of serratamic acid for 50% hemolysis was 0.17 mM at 37 degrees C for 0.2% human erythrocyte suspension in the liposomes which composed of phosphatidylserine, cholesteryl nervonate and serratamic acid (1:0.50:0.37 by mol). 4. The hemolysis was shown specifically in human, horse and rabbit erythrocytes containing phosphatidylcholine, but not in sheep or bovine erythrocytes lacking phosphatidylcholine. 5. The hemolytic activity was strongly inhibited by the exogenous addition of phosphatidylcholine. It was suggested that the hemolysis by serratamic acid-containing liposomes was specific for phosphatidylcholine-containing erythrocyte membranes.