Our study was undertaken to demonstrate the efficacy of digital plethysmography using a strain gauge plethysmograph in the assessment of the reactive hyperemic response. We studied patients with Raynaud's phenomenon with and without associated connective tissue disorders. Reactive hyperemic response was examined in 27 normal subjects and 19 patients with Raynaud's phenomenon at 12-14 degrees C, 20-22 degrees C and 37-40 degrees C. In the normal subjects reactive hyperemia was greatest at 20-22 degrees C. In 19 patients with Raynaud's phenomenon, the pulse waves were smaller at 20-22 degrees C than in normal subjects and the response was seen in only 5 of 19 patients. At 12-14 degrees C reactive hyperemic response was usually absent and at 37-40 degrees C it was evident in 9 patients. Nifedipine was given to 11 patients (5 mg TID for 4 weeks) and in 10 of them, reactive hyperemic response was restored at 20-22 degrees C.