AbstractThe effect of local controlled cooling on the digital systolic blood pressure in the hand was studied in 25 healthy volunteers and 25 patients with Raynaud's syndrome.Arterial systolic pressure was indirectly measured using a digital cuff over the proximal phalanx and a photoplethysmographic probe over the digital pulp to detect pulsation. Pressures were measured after occlusion of the circulation (cuff at 180 mmHg) for 5 minutes with water circulating initially at 30°C and then at 10°C. An airfilled cuff was used simultaneously on a control finger. The digital systolic pressure at 10°C in the patients was significantly lower (P<0·001 Mann–Whitney U test) than in the normal volunteers whilst calculation of the percentage change in pressure induced by cooling the digit to 10°C allowed complete separation between both groups. The range in the controls was +2 per cent to −26 per cent and in the patients, −33 per cent to −100 per cent. The test gives reproducible results (coefficient of variation 5–11 per cent) and offers an objective method of identifying patients with excessive vasospasm due to a cold stimulus. It may prove useful in studying natural history and the effect o