We investigated post-ischemic hyperreactive cutaneous blood flow in patients with primary Raynaud's phenomenon and Raynaud's phenomenon secondary to systemic sclerosis (SSc). Reactive hyperemia was measured over a locally warmed area of skin, using a laser Doppler flowmeter, following 5 minutes of suprasystolic occlusion of blood flow. We found that patients with primary Raynaud's phenomenon had normal post-ischemic blood flow compared with normal controls. In contrast, patients with SSc had reduced levels of baseline and peak blood flow compared with either the primary Raynaud's phenomenon patients or the normal subjects. Infusion of carbaprostacyclin, a potent prostacyclin analog vasodilator, did not increase blood flow in the SSc patients, nor did it restore the reactive hyperemic response. These findings are consistent with the hypothesis that patients with the nonvasoconstricted condition of SSc have fixed structural defects that limit cutaneous microvascular blood flow.