UNLABELLED In 34 subjects (29 subjects vibrations exposed and 5 controls), the variations of seric levels of endothelin (Et) after Cold Test were investigated, while vasomotor modifications were monitored and recorded by forefinger volumetric pulsoplethismography. Blood sampling for Et dosage (from dorsal vein of the hand) was done in 17 subjects after 2' Cold Test and in 17 subjects after 5' Cold Test. RESULTS 1) Et levels are always increased after Cold Test but level increase is statistically significant only after 5' Cold Test. 2) There is no evidence of relations between Et level increase and pulsoplethismographic alterations showing acral vasospasm. It is evident that in Raynaud phenomenon Et increase is not the only factor but takes part in the occurring of this acrosyndrome. When endothelium has a reduced activity opposing cold induced vasoconstriction, seric Et increased level may represent a biohumoral factor enhancing entity and duration of vasospasm.