Background: Sensitivity of interleukin-8 (IL-8) in detecting early-onset bacterial infection (EOBI) is high. A high percentage is bound to nonspecific receptors on erythrocytes which can be determined via cell lysis. We have shown detergent-lysed whole blood (DLWB) IL-8 to be superior to plasma IL-8 in detecting EOBI. Methods: To evaluate influence of pre- and perinatal factors on plasma and DLWB IL-8 concentrations, IL-8 was determined via ELISA (Immulite) in 146 noninfected newborns with risk factors for EOBI at two different time periods: 0–6 (group I) and 24–30 h (group II) after birth. The influence of gender, mode of delivery, gestational age and hematocrit was evaluated. Results: While we found no influence of gender or gestational age, hematocrit was positively correlated with IL-8 plasma concentration (group I: r = 0.33, p < 0.001; group II: r = 0.30, p <0.01). IL-8 plasma concentrations after primary versus secondary cesarean section were lower (p < 0.05). Gestational age was correlated with DLWB IL-8 concentrations (group I: r = 0.46, p < 0.001; group II: r = 0.28, p < 0.001). Conclusion: Plasma IL-8 concentrations were positively correlated with hematocrit, whereas DLWB IL-8 concentrations increased with gestational age. This may be relevant to the interpretation of IL-8 in preterm infants and infants with anemia, polyglobulia or hematolytic diseases.