Leukocytes isolated from patients with polycythemia vera (PCV), a panmyelopathy, have increased metabolic activity during the resting and phagocytizing states. Phagocytes from patients with PCV were studied by counting particle ingestion, measuring hexose monophosphate shunt (HMP) activity by the conversion of glucose-1-14C to 14CO2, and determining O2 consumption and nitroblue tetrazolium (NBT) reduction. Phagocytosis of polystyrene particles was increased. Resting glucose-1-14C activity was 6.9 ± 2.7 nmoles of glucose oxidized per hour per 5 x 106 phagocytes in normal and 16.4 ± 7.6 nmoles in polycythemia vera phagocytes. Hexose monophosphate shunt following phagocytosis increased to 50.6 ± 10.4 nmoles in normal and 91.7 ± 17.0 in polycythemia vera phagocytes (p < 0.005). Oxygen consumption was 3.6 ± 0.2 µl/hr/5 x 106 phagocytes in resting and 11.4 µl/hr/5 x 106 phagocytes in stimulated controls as compared to 4.8 ± 0.2 µl in resting and 18.4 µl in phagocytizing PCV cells (p <0.001). The reduction of NBT by leukocytes was increased in all resting polycythemia vera phagocytes as compared to control phagocytes. The cells from some patients had increases in the amount of NBT reduced during phagocytosis. Phagocytes from four severly infected patients had increases in HMP activity in both resting and phagocytizing cells similar to those found in noninfected PCV phagocytes. Although the increased metabolic activity associated with phagocytosis can be explained by increased particle ingestion, the increased activity of resting PCV cells suggests other metabolic abnormalities perhaps related to the age of the phagocyte.