A decreasing activity of the vascular bed upon changes in vascular transmural pressure and changes in arterial perfusion pressure head was observed from hand to fingers and from subcutis to cutis in patients suffering from generalized scleroderma. These findings are expressions of deteriorating vascular smooth muscle function. The reactive hyperemia response was decreased in subcutaneous as well as cutaneous tissue in patients fingers and in 4 of 7 patients the response was absent from the finger tip. The reactive hyperemia response of the patients resembled responses obtained in normal fingers during decrease in local perfusion blood pressure, during local cooling or after infiltration of norepinephrine around the digital arteries. This implied an increased digital artery resistance in generalizing scleroderma. A positive feed back loop between cooling, increase in digital artery resistance, increase in blood viscosity and a passive vascular bed is proposed as an important factor in Raynaud's phenomenon.