A five-chambered pneumatic vinyl sleeve was used to determine the optimum pressure range of graduated, static, external compression of the lower limb, which would be most beneficial in increasing deep venous velocity. The effects of four different ranges of pressure upon deep venous velocity (technetium-99), calf muscle blood flow (xenon-133) and subcutaneous tissue flow (sodium-24) were measured in recumbent patients. The pressure range 18, 14, 8, 10, 8 mmHg produced a significant increase in mean deep venous velocity (P less than 0.02) without any consequent impairment of either calf muscle blood flow or subcutaneous tissue flow. A higher pressure range of 30, 26, 14, 18, 12 mmHg also produced an increase in mean deep venous velocity, but caused a significant impairment of calf subcutaneous tissue flow.