• Enzymes released from bacteria can alter the surfaces of RBCs rendering them susceptible to destruction by antibodies present in a high percentage of adult plasmas. Such RBC alterations were observed in four of 20 consecutive cases of radiologically proved necrotizing enterocolitis. Involved infants were seriously ill, three of four demonstrating bowel perforation. Bacteria of the genus Clostridium were isolated from blood or peritoneal fluid in three of four affected patients and elaborated appropriate RBC-altering enzymes in vitro. Two patients who had received plasma-containing products experienced notable hemolysis. Patients treated with washed products and plasma protein fractions lacking immunoglobulins had no hemolytic problems. The alteration of the RBC membrane is easily detected by a rapid, simple lectin agglutination test.