Severe haemolysis is an unusual occurrence in association with necrotising enterocolitis (NEC). Activation of the Thomsen-Friedenreich (T) antigen on the neonatal erythrocytes is proposed as the mechanism. This haemolytic process is precipitated by transfusion with serum-containing blood products, which should therefore be avoided. Once haemolysis has become established the outcome is usually fatal. This report describes the management of four neonates who had established haemolysis complicating severe NEC. T activation was confirmed in two infants, but could not be tested for in the other two. Exchange transfusion abolished the haemolysis in two patients, who survived. Despite reduced use of blood products the other two infants died. We believe that exchange transfusion was essential in the successful management of the infants who survived, and recommend early exchange transfusion when haemolysis complicates NEC.