Considerable experimental evidence in animals suggests that treatment with G‐CSF may have a beneficial effect in the management of severe infections in non‐neutropenic hosts. This beneficial effect is attributed to an enhancement of granulopoiesis and neutrophil function, the latter possibly involving up‐regulation of receptors on neutrophils that are involved in antibody‐mediated cytotoxicity and killing of microorganisms. We compared neutrophil function and phenotype in blood and bronchoalveolar lavage fluid (BALF) of 10 patients with severe ventilator‐dependent pneumonia, at baseline and following initiation of G‐CSF treatment as adjunct to standard therapy. G‐CSF treatment was associated with three‐fold increased blood neutrophil counts at day 3 of treatment compared with baseline counts. Mean serum G‐CSF concentration increased from 313 to 2007 pg/ml. After correction for lavage dilution effects, BALF G‐CSF levels did not differ significantly from baseline, nor did neutrophil receptor expression (FcγRI, FcγRII, FcγRIII, CR3, and L‐selectin) or indicators of neutrophil function such as respiratory burst activity, phagocytosis and killing of Candida albicans in BALF or blood. The mortality in this group of patients was 30% and compared favourably to the APACHE II‐derived predicted mortality of 60%. We conclude that the possible therapeutic benefit of G‐CSF administration in the early phase of severe bacterial pneumonia is not readily explained by its effect on baseline indicators of neutrophil function or receptor expression.