Digital angiography provides a convenient means to quantify the progression of a contrast medium bolus injected into a coronary artery throughout the myocardium, which in turn yields information on myocardial perfusion. Sixteen patients presenting a single critical proximal stenosis (estimated diameter reduction greater than 80%) on either the left anterior descending coronary artery (LAD) or the left circumflex coronary artery (LCX) were studied. First, 12 consecutive end-diastolic images of an ECG-triggered intracoronary injection of 4 ml of iopamidol were acquired on 60 degree left anterior oblique projection under basal conditions. This was repeated 30 s after intracoronary injection of 12 mg of papaverine. For each image sequence, a densogram was computed in each pixel by fitting a curve through its 12 consecutive intensity values. The 'time of maximal pixel opacification' (TMAX) and the 'mean ascending time' (TMAT), expressed in cardiac cycles, were determined from each curve. Two myocardial regions of interest (ROI) were defined for each patient, one in the perfusion bed of the LAD, the other in the bed of the LCX. The mean values of TMAX and TMAT in each ROI were computed, at rest and during hyperemia. At rest, the mean values of TMAX and TMAT obtained from the ROI associated to the stenosis artery were not significantly different from the values obtained in the ROI associated with the intact artery. During hyperemia, a significant decrease of the mean TMAX and TMAT was observed in the normally perfused regions (p less than 0.001). The rest to hyperemia ratios of both TMAX and TMAT mean values were considered to be indices of coronary flow reserve.(ABSTRACT TRUNCATED AT 250 WORDS)