Plasma IL-8 is a diagnostic parameter of early-onset bacterial infection (EOBI) in neonates but has a short half-life. The detergent-lysed whole-blood (DLWB) IL-8 consists of both extracellular and cell-bound IL-8. The objective of this study was to investigate kinetics of plasma and DLWB IL-8 in healthy newborns and those with suspected EOBI and to test the hypothesis that determination of DLWB IL-8 results in higher sensitivity for EOBI detection. Sixty-one neonates with clinical and serologic signs of EOBI composed the study group; 188 neonates with risk factors but without EOBI served as control subjects. IL-8 concentrations were determined in plasma and DLWB. In the control group, DLWB IL-8 concentrations were 280-fold higher (9599 pg/mL; SD 4433) up to 24 h post partum than corresponding plasma levels (34.2 pg/mL; SD 18.1). The sensitivity of DLWB versus plasma IL-8 for EOBI was 0.97 versus 0.71 after 6 h and 0.70 versus 0.32 after 24 h. Corresponding values for specificity were 0.95 versus 0.90 after 6 h and 0.92 versus 0.99 after 24 h. After 24 h, the negative predictive value for DLWB versus plasma IL-8 was 0.80 versus 0.66. DLWB IL-8 showed a higher sensitivity for EOBI within 6 h after first clinical suspicion than plasma IL-8. It also remained elevated longer. Our results suggest that DLWB IL-8 results in a higher sensitivity for EOBI.