1. Reliable objective tests for the diagnosis and grading of vasospasm would be helpful in the assessment of patients with Raynaud's syndrome. 2. Measurements of finger blood flow at local finger temperatures from 32 degrees C down to 20 degrees C did not reliably distinguish between patients with Raynaud's syndrome and matched control subjects. 3. Using laser Doppler flowmetry to detect blood cell flux in fingertip skin, there was no significant difference (Wilcoxon's signed rank test) in the finger systolic blood pressure of 28 patients with Raynaud's syndrome and their matched controls when the fingers were warm at 32 degrees C. 4. Absence of flux was considered to indicate complete vasospasm and the degree of cooling required to abolish flux indicated the severity of the vasospastic condition in an individual patient. 5. Finger cooling for 5 min did not significantly alter finger systolic blood pressure in the control subjects, but abolished blood cell flux in the fingertip skin of 27 of the 28 patients with Raynaud's syndrome. 6. A grading scale was derived from the flux measurements. There was a significant correlation (r = 0.75, P less than 0.001) between the grading of disease severity as judged by the flux test and the clinical grade as assessed before the laboratory visit. 7. There was one false-negative result in the 28 patients with Raynaud's syndrome tested and no false-positive results in 28 matched control subjects. 8. This type of testing may prove helpful in the diagnosis and grading of vasospastic disorders.