In 18 consecutive transplant patients with normal coronary angiograms and without calcium blocker therapy, and in 20 controls, we measured the diameters of the left anterior descending artery using quantitative coronary angiography. Measurements were effected on the frames recorded 5 min or more after intravenous administration of 0.4 mg methylergometrine, and 2 min after subsequent 2 mg bolus intracoronary isosorbide dinitrate administration. The arterial vasodilatory capacity was defined as the ratio of the difference of the largest and smallest arterial diameters and the smallest diameter. We observed normal vasoconstriction of the different coronary arterial segments. Coronary arterial diameter decrease from basal state was about 8% and was more pronounced at the distal segments of the left anterior descending artery. There was no difference of vasodilatory capacity between transplant patients and controls for the proximal and middle portion of the left anterior descending artery, while the difference was highly significant for the distal portion. In eight patients, the decrease of the vasodilatory capacity was beyond the lower limit of the normal range of values. The significance of those quantitative angiographic abnormalities is still unproven. They could be due to early vasomotor capacity blunting after transplantation and to late structural alterations of distal coronary vessels in cardiac transplant patients.