Variant X-linked chronic granulomatous disease (CGD) is characterised by a decreased but still measurable respiratory burst and cytochrome b content of phagocytes resulting in a clinically milder form of the disease. We examined the in vivo effect of recombinant human granulocyte-macrophage colony stimulating factor (rh-GM-CSF) on the neutrophil functions of a patient treated for liver abscess. The number of white blood cells was markedly increased at the highest dose of GM-CSF injected (30 micrograms/kg per day). This was mainly due to a large increase in eosinophils and to a lesser extent in neutrophils. No change in the deficient neutrophil respiratory burst nitroblue tetrazolium (NBT)-reduction, superoxide (O2-)-production and cytochrome b content was observed during 6 weeks of therapy with increasing doses of GM-CSF. No significant clinical improvement of the liver abscess was observed during treatment with GM-CSF.