SUMMARYBlood flow was measured in patients with Raynaud's phenomenon, systemic sclerosis and in normal controls by venous occlusion plethysmography on the forearm and calf, and changes in blood flow in the finger were followed by calorimetry.Intravenous naftidrofuryl oxalate (praxilene) improved blood flow to the skin of the finger as measured calorimetrically in seven of sixteen patients with Raynaud's phenomenon and systemic sclerosis. The drug markedly reduced blood flow in the finger in all ten normal control subjects. However, naftidrofuryl increased blood flow as measured by venous occlusion plethysmography in the leg both of normal subjects and of those with Raynaud's phenomenon. In addition to these findings, no significant change in blood flow in response to the drug was observed in the forearm. The reasons for these regional differences are discussed and considered to be due to redistribution of blood flow as a result of differences in pharmacological receptor activity in different parts of the body and possibly also due to effects of central control.