Peripheral blood polymorphonuclear neutrophil (PMN) function has been investigated for 46 children with kwashiorkor (without overt infection) in the Ivory Coast, West Africa. In vitro chemotactic response, candidacidal activity, and kinetic studies of metabolism during phagocytosis have been performed. Postphagocytic morphological events were evaluated by electron microscopy. The reduction of nitroblue tetrazolium (NBT), measurement of enzyme activities, activity of glycolysis, and hexose monophosphate shunt (HMS) activity were assessed. The extent of iodide incorporation into trichloracetic acid (TCA)-precipitable protein by phagocytizing PMN'S and thyroid hormone degradation were measured. Chemotactic response was reduced at early time intervals (30, 60, and 120 minutes) and reached control values after 180 minutes. Whereas PMN's of controls killed 32.13 +/- 11.10 per cent of Candida albicans after 60 minutes, PMN's from kwashiorkor patients killed 18.55 +/- 7.74 per cent (p less than 0.01). HMS activity for resting PMN's of kwashiorkor children was higher than for controls, and during particle ingestion the extent of stimulation was comparable to controls. Electron microscopic assessment of phagocytic vacuole formation and degranulation showed no difference between PMN's from kwashiorkor and and control subjects. Incorporation of 131 I into TCA-precipitable proteins by phagocytizing PMN's from kwashiorkor children was reduced in compraison to controls, with either viable or heat-killed lactobacilli. No impairment in thyroxine (T4) degradation was observed for PMN's from kwashiorkor cases. PMS's from kwashiorkor patients show toxic granules, Dohle bodies, evidence of high baseline NBT reduction, and glucose decarboxylation. Functional studies indicate impaired kinetics of chemotaxis, diminished candidacidal activity, and reduced iodination. Enzymatic activities of resting cells are normal. Lactate production, HMS activity during phagocytosis, and morphological events are not impaired. Thus, impaired in vitro microbicidal activity, increased resting metabolism, and decreases iodination by PMN's may be related to the high incidence of infection in kwashiorkor.