With the use of a multifinger photoplethysmography system, finger systolic blood pressures were measured before and after cooling in patients with Raynaud's disease. In 30 patients with arteriographically documented arterial obstructions, significantly low digital pressures were found in 91% of fingers with cold sensitivity. In this group of patients a mean decrease in finger pressure of 12.3% occurred during cooling. In a group of 32 patients with Raynaud's phenomenon from unknown causes (primary Raynaud's disease) normal finger pressures were found in 147 (97%) of 152 fingers with cold sensitivity. However, in patients with primary Raynaud's disease, significant lowering of finger pressures was observed after cooling, with an average maximal decrease of 59.2%. The multifinger photoplethysmography method promises to be a reliable instrument for objective measurement in patients with Raynaud's phenomenon.