Using reverse transcriptase-polymerase chain reaction, products corresponding to mRNA encoding endothelin-A and -B (ETA and ETB) receptors were demonstrated in human coronary arteries and veins with intact endothelium and in endothelium-denuded human coronary arteries. Vasomotor responses were studied on isolated segments of human epicardial coronary arteries and veins at resting tension and after precontraction with U46619. In both arteries and veins, endothelin-1 (ET) induced strong and potent contractions, and preincubation with different concentrations of the non-selective ETA/ETB receptor antagonist PD 145065 caused a rightward shift of the concentration-response curves without significantly changing maximum responses (pA2 value 6.7 arteries, 7.4 veins). The ETB receptor agonist IRL 1620 induced no contraction of arteries or veins at resting tension, but induced weak relaxation of all arteries and most precontracted veins, the relaxation being endothelium-dependent in arteries. ET at low concentrations induced weak relaxations of most precontracted arteries, but no veins. In conclusion, mRNA encoding ETA and ETB receptors is present in human coronary arteries and veins, ETA receptors mediating contraction and ETB receptors mediating relaxation. In arteries, mRNA for both receptor types was detected in the media, but ETB receptor-mediated relaxation was endothelium-dependent.