Abstract Objective: To examine whether perinatal complications induce the production of macrophage-colony stimulating factor (M-CSF), we have compared M-CSF levels in the cord blood between normal neonates and neonates with complications. Methods: The M-CSF levels were determined by enzyme-linked immunosorbent assay (ELISA). Results: In 54 normal neonates, the M-CSF level was 1859±287 U/ml (mean±S.D.), being significantly higher than the serum M-CSF level in normal adults (697±132 U/ml). Compared with the M-CSF levels in normal neonates, significantly higher levels were evidenced in neonates with perinatal complications including premature rupture of the membranes, neonatal asphyxia, meconium staining of the amniotic fluid and maternal anemia. However, no difference in M-CSF concentrations was observed irrespective of complication types; furthermore, the M-CSF level was highly correlated with the leukocyte counts in the neonates with complications, but not in normal neonates. Incidentally, CRP levels were within normal limits in most of these neonates. Conclusion: M-CSF levels in the cord blood from neonates with premature rupture of the membranes, neonatal asphyxia, meconium staining of the amniotic fluid and maternal anemia were significantly higher than those in the cord blood sampled from normal neonates. The stress given to neonates may account for the higher M-CSF levels rather than infections.