1. The response of hand blood flow to a measured controlled cold stimulus was determined using venous occlusion plethysmography in normal subjects and patients exhibiting Raynaud's phenomenon.
2. Comparisons of percentage and absolute falls in hand blood flow, and also the recovery times after removal of the cold stimulus, were made in both the normal subjects and the patients and found to be similar.
3. The nature of the abnormality causing Raynaud's phenomenon was not elicited, but it did not appear to be due to an increased sensitivity of the hand vasculature to cold.