The influence of colony-stimulating factors (CSFs) on the monocyte functions of 32 patients with refractory testicular cancer receiving high-dose chemotherapy followed by autologous bone marrow transplantation (ABMT) was tested. Eight patients were treated as a control group without CSF therapy, 12 patients received recombinant human granulocyte-macrophage-CSF (rhGM-CSF), and 12 patients received recombinant human granulocyte-CSF (rhG-CSF). For the assessment of monocyte activation induced by CSF expression of major histocompatibility complex (MHC) class I and II antigens, production of tumor necrosis factor (TNF) and monocyte-mediated cytotoxicity against tumor cell targets were chosen. Monocytes from patients with GM-CSF therapy showed a significant increase in MHC class I and II antigen expression as compared to patients without CSF treatment (p< 0.001). A significant increase in the expression of MHC class I was seen in monocytes from patients under G-CSF treatment, whereas no change of class II antigens was noticed. Production of TNF and monocyte-mediated cytotoxicity against U937 tumor cells was significantly increased in monocytes derived from patients receiving GM-CSF, as compared to those from the control group, while no effect was detectable in monocytes from patients with G-CSF therapy. However, after in vitro stimulation with interferon-gamma (IFN-gamma), monocytes derived from GM-CSF as well as from G-CSF treated patients responded with a significantly higher TNF-production and cytotoxicity than monocytes from control patients.