Electrical skin resistance and digital skin temperatures were measured in 33 patients with systemic sclerosis and 15 patients with Raynaud's phenomenon, and contrasted with measurements in normal control subjects and patients with other diseases. Scleroderma patients failed to show evidence of sympathetic nervous system hyperactivity by these techniques. Indeed, skin resistance findings provided some evidence for sympathetic hypoactivity in the fingertips. involvement of the sympathetic nervous system in scleroderma, if present, appears to be a secondary feature of the disease. "Sympathetic underactivity" might be a compensatory mechanism to increase blood flow in areas of severe peripheral vascular disease; the poor results with sympathectomy are thus not surprising. Catecholamine and monoamine oxidase (MAO) depletion secondary to sympathetic hypoactivity might explain the increased sensitivity to catecholamines and serotonin in the scleroderma patient.