The effect of M-CSF on the differential WBC counts of SW mice. M-CSF, 4 mg/kg/d, was administered to SW mice for 5 days, on days 1 to 5. Blood samples were obtained and the total WBC and platelet counts were determined. Percentages of monocytes, neutrophils, and lymphocytes were determined from buffy coat cytofuge preparations. Neutrophils and lymphocytes were identified by standard morphologic characteristics. Monocytes were identified by histochemical staining, using M-CSF conjugated to alkaline phosphatase to bind to the M-CSF receptor. Absolute total numbers of nucleated WBC are indicated by the height of the bars. The total WBC count was significantly increased only on day 8 (#, P < .05). The percentages of monocytes on each day are indicated in parentheses at the top of each bar. On day 3 (n = 6) and day 5 (n = 5), the total numbers of monocytes were significantly different from the control (n = 4) (★, P < .05). On day 8 (n = 6) and day 10 (n = 6), total numbers of monocytes were not different from the control.