Neutrophil microbicidal activity. Neutrophil bactericidal activity was measured as described in Materials and Methods. At a 1:1 ratio (bacteria:neutrophil) (A), the PMN bactericidal capacity was normal after G-CSF therapy in vivo (normal, n = 15; treated volunteers, n = 5). At 10:1 ratio (bacteria:neutrophil), the PMN bactericidal capacity was reduced at all time points after G-CSF treatment in vivo (B). The difference reached statistical significance at 30 minutes (*P = .002) and at 90 minutes (**P = .028). Results are expressed as a percentage of the initial bacterial count and represent mean ± SEM (normal, n = 13; treated volunteers, n = 3).