- Background. Neutrophils play a critical role in host defense against a variety of microbial pathogens. There is much information to suggest a role for vitamin C in the physiology of neutrophils. Thus, the effects of vitamin C treatment were studied in a patient with a history of recurrent furunculosis who showed altered neutrophil functions. Methods. Superoxide generation was measured by cytochrome C reduction. Phagocytosis of opsonized zymosan by neutrophils and chemotaxis on agarose plates were determined. Results. Chemotaxis, phagocytosis, and superoxide generation of the patient's neutrophils were significantly lower than those of the matched control. Treatment with vitamin C (500 mg/day) for 30 days caused a dramatic clinical response and a significant improvement of all three neutrophil functions to values similar to those of the controls. Conclusions. We suggest that the patient described here had a temporary defect in neutrophil functions. The treatment with vitamin C probably prevented neutrophil oxidation, thus contributing to recovery of neutrophil function and arrest of furunculosis.