Finger blood flow was measured by laser Doppler flowmetry in 15 patients with Raynaud's phenomenon (RP) due to systemic sclerosis (SS), and 15 normal controls. Measurements were performed in a temperature controlled room at 28 degrees C. The blood flow in the patients was significantly lower than in the controls (P less than 0.001). After hand warming in water at 35 degrees C for 10 min, blood flow in the patients and controls did not differ significantly. Following this, the response to a standardized cold stress produced similar falls in both groups to levels that were not significantly different and these occurred over a similar time course. After cold stress ended, there was recovery of blood flow in both groups, and blood flow after 20 min was not significantly different between the two groups. The induced vasodilatation persisted, in those patients in whom it was remeasured, for at least 2 h. Repeating the experiments at a room temperature of 24 degrees C produced similar results. This indicates that considerable vasodilatation is possible in these patients, and can be produced by simple means. It also indicates that local and central thermoregulatory reflexes are intact. Cold induced symptoms in patients with SS are related to low resting blood flow, not to cold sensitivity, and simple warming may provide a useful treatment.