Functional effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) were prospectively measured by harvesting blood samples from 51 oncology patients (21 who were receiving no cytokines, 14 receiving rhGM-CSF, and 16 who were receiving rhG-CSF) just before cytotoxic chemotherapy (baseline) immediately before the last cytokine dose (pre), 2 hours after the last cytokine dose (post), and 48 hours after the pre period (follow-up). Neutrophils and monocytes were separated and functional effects were measured by comparing cell-kill percentages, as determined by a microbial cell-kill assay against Staphylococcus aureus and Candida albicans. Optimal cell concentrations (2 x 10(6) monocytes/ml; 4 x 10(6) neutrophils/ml) and effector-to-cell ratios (1:50) were initially determined with blood samples harvested from 23 healthy volunteers. Results in oncology patients indicated that rhGM-CSF improved monocyte-killing activity against S. aureus at follow-up, compared with controls (p = 0.0094) and compared with monocytes from rhG-CSF-treated patients at the post period (p = 0.014). Cell-killing percentage of the rhGM-CSF-treated patients was also enhanced against C. albicans during the post period, compared with controls (p = 0.011) and rhG-CSF-treated patients (p = 0.067). Neutrophil activity was not altered by either cytokine. In conclusion, monocyte-induced microbial killing was enhanced in oncology patients receiving rhGM-CSF after cytotoxic chemotherapy, compared with patients receiving rhG-CSF or no cytokines. No differences in neutrophil activity were observed between patients receiving either cytokine.