It is well known that necrotizing enterocolitis (NEC) is less frequent in newborns being fed human breast milk. Since recent studies indicated that platelet-activating factor (PAF) plays an important role in pathogenesis of NEC, this study was conducted to investigate the PAF levels in human milk. Colostrum and mature human milk (samples obtained in the third week) of three groups of mothers were investigated. The first group had given birth within less than 32 weeks, the second between 33-37 weeks and the third group after 38 weeks of gestation. The PAF levels in colostrum of all three groups were similar (0.95 +/- 0.57, 1.05 +/- 0.52 and 1.19 +/- 0.64 ng/ml, respectively). Mature human milk in groups I and II had similar PAF levels (1.16 +/- 0.54 and 1.21 +/- 0.60 ng/ml, respectively), however, mature human milk in group III had a significantly higher PAF concentration (2.04 +/- 0.59 ng/ml) than both groups' levels. However, this phenomenon by itself does not explain the protective effect of human milk against NEC.