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To assess endothelin-1 (ET-1) response to cold stimulation in essential acrocyanosis (EA), the authors measured ET-1 plasma concentrations in 6 patients with EA (6 women, age range seventeen to thirty-seven years) and in 6 controls (5 women, 1 man, age range twenty-one to thirty-seven years) before and after cold challenge by unilateral hand immersion in water bath at 13°C for five minutes. The contralateral upper limb was considered as control. Blood samples were simultaneously drawn from an antecubital vein in the cooled side and in the contralateral upper limb at baseline, at the end of cooling, and at ten and ninety minutes after cooling was begun. Plasma ET-1 was deter mined by a radioimmunoassay system. Results are mean ±SD. Baseline ET-1 was higher in patients with EA (5.1 ±0.3 pmol/L) than in controls (1.9 ± 0.1 pmol/L, P < 0.001). After hand cooling, ET-1 in the cold-exposed upper limb rose in patients with EA to a peak value of 7.2 ±0.7 pmol/L, which was greater than that observed in healthy subjects (2.7 ±0.4 pmol/L, P < 0.001). The absolute increase in ET-1 plasma concentrations from baseline to peak value was significantly higher in patients with EA than in controls (2.1 ±0.3 vs 0.8 ± 0.2 pmol/L, respectively, P < 0.001). In patients with EA, but not in controls, the rise in ET-1 plasma concentrations was still detected ninety minutes after cooling. The same time course of the plasma ET-1 concentrations was observed in the noncooled upper limb, but the increases in ET-1 at different times after cold stimulus were smaller than in the cold-challenged upper limb in both groups (P < 0.001). In conclusion, the results demonstrate that in patients with EA, baseline plasma levels of ET-1 are enhanced and are further increased by cooling until ninety minutes after cold challenge. This rise in plasma ET-1 could contribute to potentiating and prolonging cold-induced vasoconstric tion/vasospasm and/or could be a marker for endothelial damage in EA.