1. The saphenous vein (SV) and internal thoracic artery (ITA) are the most commonly used conduits for coronary artery bypass surgery (CABS). The ITA shows better long term patency than the SV, at least in part due to their different responses to agonists, as well as physical differences between the ITA and SV at the time of grafting. 2. Angiotensin II (A II), a potent endogenous vasoconstrictor circulates at augmented levels during and after CABS, but little is known about the effects of A II on the SV and ITA. 3. We studied the contractile effects of A II on SV and ITA as intact rings from a heterogeneous group of patients undergoing CABS. Two groups of SV samples were studied; freshly excised SV (FSV) with no further manipulation and SV that had been surgically prepared for use as a bypass conduit (PSV). We also assessed the function of the endothelium in FSV, PSV and ITA, by measuring the relaxation of preconstricted rings to bradykinin. In some tissues endothelial presence was examined histologically. 4. Surgical preparation of SV affected the contractile ability of the smooth muscle, as PSV contracted less than FSV to potassium chloride (KCl, 90 mM) (P < 0.0001). Loss of endothelial function was seen in 25% of FSV, 50% of PSV and 33% of ITA. 5. A II caused concentration dependent contractions in all rings, over the same concentration range (1 nM-100 nM). In rings of FSV the presence of functional endothelium attenuated the response, median values with endothelium being less than half that without endothelium (P < 0.0007, at 100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)