Inflammatory cytokines interleukin-1beta (IL-1beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were measured in the serum of healthy, term neonates on the first (N1), fifth (N5) and 40th (N40) day after birth, compared with those in maternal serum (MS), umbilical cord (UC) and in adult controls. All three cytokines were significantly elevated in N1 and N5, compared with those in UC and adults (P < 0.0001). IL-1beta and IL-6 declined significantly from N1 to N40 (P < 0.0001), while TNF-alpha increased significantly from N1 to N5 and declined thereafter. TNF-alpha values in UC were significantly higher than in adults, but lower than in N40 (P < 0.0001), while IL-1beta and IL-6 values in UC did not differ from those in N40 and in adults. IL-1beta and IL-6, but not TNF-alpha values in MS were significantly higher than those in controls (P < 0.0001). IL-1beta values in MS were significantly higher than those in N1 (P < 0.0001), while those of IL-6 and TNF-alpha were significantly lower (P < 0.0001). Moreover, IL- 1beta values were dependent on the mode of delivery in N1 (P < 0.001), in MS (P < 0.02) and in UC (0.03), while IL-1beta and TNF-alpha values in N1 were strongly interrelated (r = 0.7; P < 0.01). In conclusion, the increased values of IL-1beta, IL-6 and TNF-alpha during the perinatal period might reflect a newborn immune response to the stress of delivery and to environmental changes after birth.