Because previous investigations have suggested that platelet activating factor and tumor necrosis factor-alpha (TNF-alpha) are important mediators of experimental necrotizing enterocolitis in the rat, we measured platelet activating factor, acetylhydrolase (the platelet activating factor breakdown enzyme), and TNF-alpha in the plasma of 12 human neonates with necrotizing enterocolitis and eight age-matched control subjects with similar gestational ages, postnatal ages, and weights. Almost all patients with necrotizing enterocolitis had elevated plasma platelet activating factor values (18.1 +/- 3.6 ng/ml vs. 3.1 +/- 0.9 ng/ml in control subjects, p less than 0.01). Plasma acetylhydrolase activity was lower in patients than in control subjects (10.6 +/- 0.7 nmol/ml/min vs 23.0 +/- 1.4 nmol/ml/min, p less than 0.01). Plasma TNF-alpha concentration was significantly elevated in patients with necrotizing enterocolitis (136 +/- 75 U/ml vs 1.5 +/- 0.8 U/ml, p less than 0.05), although the individual variation was high. There was no correlation between individual TNF-alpha and platelet activating factor levels. We conclude that platelet activating factor and TNF-alpha are elevated in patients with necrotizing enterocolitis and that suppressed platelet activating factor degradation contributes to the increased platelet activating factor levels; platelet activating factor and TNF-alpha may contribute to the pathophysiology of necrotizing enterocolitis.