Neutrophil polymorphonuclear leucocytes and macrophages contain 10–40 times increased intracellular ascorbate concentrations compared to plasma. A slight decrease of ascorbate content could be observed in total white blood cells and in monocytes upon stimulation with opsonized zymosan. These decreases were more pronounced in peritoneal and alveolar macrophages from rats. In patients with rheumatoid disease whose phagocytes are exposed to a constant challenge, significantly lowered intracellular ascorbate contents were found in neutrophils and mononuclear cells. Surgical and thermal trauma in rats depressed intracellular ascorbate levels in peritoneal macrophages. These results are indicative of an essential role ascorbic acid plays in phagocytic cells.