We studied the clinical usefulness of the VCS parameters (mean channels of cell volume, conductivity, and light scatter) in reactive neutrophils for predicting acute bacterial infection, which are obtained by the Coulter LH 750 hematology analyzer (Beckman Coulter, Fullerton, CA) during automated differential counts. Peripheral blood samples from 69 patients with positive blood cultures for bacteria and 35 control subjects were studied. We observed a significant increase in the mean channel of neutrophil volume (MNV) from septic patients compared with control subjects (156+/-13.5 vs 143+/-4.8; P<.001). The mean channel of neutrophil light scatter was decreased significantly in patients (140+/-10.1 vs 146+/-7.3; P=.002). An elevation of the MNV was associated with a higher WBC count and percentage of neutrophils and was present even in patients who did not have leukocytosis or neutrophilia. With a cutoff of 150 for the MNV, a specificity of 91% and sensitivity of 70% were achieved. As a quantitative, objective, and more sensitive parameter, we believe that the MNV has a potential to be an additional indicator for acute bacterial infection.