OBJECTIVE Frequent use of vibrating tools may lead to typical attacks of Raynaud's phenomenon (RP). The present study assesses the feasibility of the use of thermographic measurements of blood rheometry in the diagnosis of vibration-induced white-finger (VWF) syndrome. SUBJECTS AND METHODS We studied 38 patients that were suffering from RP (primary RP, n=29; VWF, n=9) and 13 controls (six men and 45 women; mean age 49.1+/-11.6 years). Superficial finger skin blood flow was assessed with an infrared thermocamera before and after exposure to heat and cold. Fibrinogen, whole-blood viscosity and erythrocyte aggregation at different shear rates and plasma viscosity were measured. MAIN RESULTS In patients with RP finger temperatures after re-warming were lower than those in controls [right hand digit (DIG) I P<0.02; DIG II-V P<0.01; left hand DIG I P<0.01; DIG II-V p<0.02], male patients with primary RP had higher Fg-values (P<0.02) and a trend to higher plasma viscosity. Patients with VWF had a trend to lower plasma viscosity than controls. Whole-blood viscosity at each shear rate was highest in patients with VWF. CONCLUSION Provocation manoeuvres are essential in the diagnosis of RP. We speculate that the decreased plasma viscosity in VWF is a compensatory physiological mechanism, probably counteracting the chronic effects of vasospasm. The rise in whole-blood viscosity could be due to endothelial injury or to a reduction in the venous blood pH level. The abnormal cold reactivity of patients with RP may be partly related to rheological factors.