The filterability rate of whole blood, the red and white blood cell sub-populations, and the erythrocyte and leucocyte count variations were studied during exercise in 20 male non-diabetic smokers, all with Stage II peripheral vascular disease (PVD), and 20 matched controls. A controlled ischaemia was induced using treadmill exercise. Blood samples were taken at rest, at the onset of calf pain and at haemodynamic recovery from peak exercise. Leucocytes were counted, separated using Ficoll-Hypaque into their sub-populations by centrifugation, and adherence to Petri dishes, re-suspended in buffer and filtered through 5 micron pore diameter filters. Whole blood filterability and the leucocyte count were significantly increased at the onset of calf pain. A significant increase was observed in the filterability of the monocyte sub-fraction and this persisted throughout the recovery period.