In a prospective study, levels of interleukin-1 beta (IL-1 beta), interleukin-6) (IL-6), and tumor necrosis factor (TNF) were measured in a blind fashion in cord blood plasma from 92 neonates by specific immunoassays, and were correlated with the clinical courses of the infants, including type of delivery and perinatal complications. Plasma IL-1 beta concentration was undetectable in infants born by normal vaginal delivery or elective cesarean section but was significantly increased in infants born after induced vaginal deliveries (142 +/- 68 pg/ml) or urgent cesarean section (290 +/- 21 pg/ml; both p less than 0.05 compared with normal deliveries). The IL-1 beta levels were elevated in infants with severe perinatal complications (282 +/- 116 pg/ml; p less than 0.001), whereas TNF and IL-6 levels were not related to these complications. Infants with isolated perinatal infectious complications had elevated levels of plasma IL-6 compared with those of sick neonates without infection (p less than 0.001). In contrast, TNF plasma levels and IL-1 beta production by cord blood leukocytes were decreased in infants with infectious complications alone (both p less than 0.05). These studies suggest that the levels of IL-1 beta, IL-6, and TNF in the cord plasma relate differentially to clinical complications in the perinatal period.