Oral immunoglobulin has been described as preventing necrotizing enterocolitis(NEC) in preterm infants. To prevent NEC in extremely low birth weight infants (ELBW), we have carried out oral IgG prophylaxis since April 1991. The efficacy of this prophylaxis was examined in a study comparing historical cohorts. ELBW infants delivered in the Department of Obstetrics and Gynaecology of the University of Ulm and treated until day 28 in the level III intensive care nursery, Division of Neonatology, University of Ulm were included. Cohort 1, born between 1.1.1988 and 31.3.1991, received no oral IgG and served as a control [n=84, gestational age: median 26 weeks, range 24–34; birth weight: 811 g, 490–990], cohort 2, born between 1.4.1991 and 31.12.1995 [n=137, gestational age: 26 weeks, 22–32; birth weight: 760 g, 362–995], received 6 × 100 mg/kg human IgG (Beriglobin) orally on days 1–28. NEC, stage 2a and higher according to the modified classification of Bell, was observed in 9 of 84 (10.7%) infants of cohort 1 and in 11 of 137 (8%) infants of cohort 2 until day 28. The difference did not reach statistical significance (P=0.63 Fisher's exact test).