The Effects of Phenothiazines on Human Erythrocytes: An Ultrastructural Study

S ummary . The in vitro effects of two phenothiazine derivatives on human erythrocytes have been studied by scanning electron microscopy. The induced changes were identical for both compounds and consisted of cup‐shaped deformities of the erythrocytes, sphering and membrane defects. The type and degree of alteration was a function of the concentration of the phenothiazine derivative. The demonstration of multiple surface membrane defects affords a satisfactory explanation of the haemolysis of red cells which have been exposed to chlorpromazine concentrations greater than 2.5 × 10 −4 m .