ABSTRACT. The serum acute phase reactants, C-reactive protein (CRP) and orosomucoid, rose significantly within 24 to 48 hours of presentation in infants with definite necrotizing enterocolitis (NEC) compared with the levels in infants with symptoms who tolerated early reintroduction of enteral feeds. A serum CRP value >10 mg/l within 48 hours identified infants with definite NEC with a 92% sensitivity and an 81% specificity. Serum CRP values remained elevated at 7 to 10 days in 4 infants with late septicaemia and in 4 of 5 infants with abscess or early stricture requiring surgery. Serum acute phase reactants are a potentially valuable adjunct to clinical assessment in the management of infants with suspected NEC.