['To test the hypothesis that smooth muscle cells of the human umbilical vein have vasoconstricting endothelin B (ETB) receptors.', 'In strip preparations of human umbilical veins isometric tension after exposure to the selective ETB receptor agonist sarafotoxin S6c (S6c) was compared to the tension before S6c exposure (set as 100%).', 'In intact preparations S6c induced vasoconstriction only at the highest concentration applied (10(-8)M; 149.5 +/- 12.5 vs. 100%, p < 0.05). In contrast, in endothelium-denuded preparations S6c induced vasoconstriction already at the lowest S6c concentration investigated (10(-11)M; 111.7 +/- 4.3 vs. 100%, p < 0.05).'] Do endothelin B receptors on vascular smooth muscle cells of the human umbilical vein mediate vasoconstriction?