Reactive hyperemia after 1 min of arterial occlusion was studied in back, thigh and heel skin of 40 preterm and full-term neonates using laser Doppler flowmetry. Twelve infants had clinical signs of septicemia, but normal laboratory tests at the time of fluxmetry. However, CRP, leukocyte count and the ratio of immature to total neutrophils increased during the following days and septicemia was confirmed by positive blood cultures (septic group). Seven neonates with clinical signs of septicemia had developed neither positive blood cultures nor laboratory signs (non-septic group). Fifteen were healthy neonates. In the septic neonates, time to reach maximal hyperemia, maximum post-occlusive hyperemia and recovery time of skin perfusion were increased significantly in back and thigh skin and the heal skin temperature was decreased when compared to healthy neonates. Healthy and non-septic neonates showed no significant difference in any of the parameters. We conclude that altered reactive hyperemia in the skin may be an earlier sign of neonatal septicemia than laboratory tests.