In 62 patients with angina pectoris Canadian Class III and IV, the luminal dimensions of 25 pre-PTCA and 56 post-PTCA lesions without occlusion were examined with a 4.3 F 30 MHz mechanical ultrasound imaging catheter, and analysed off-line using ultrasound cross-sectional area (U-CSA) measurements from s-VHS video images (n = 81). In addition, 42 angiographically normal coronary segments were examined. At the site of the examination, the U-CSA was integrated centrally to the leading edge echo of the inner contour of the vessel wall and the corresponding angiographic cinefilm images were analysed by edge detection using the Cardiovascular Angiography Analysis System. The obstruction diameter (at the lesion) and the mean vessel diameter (at normal sites) were used to calculate the angiographic cross-sectional area (A-CSA) assuming a circular model. U-CSA values were compared with the corresponding A-CSA values using t-test and linear regression analysis. The study showed that larger CSA are measured with ultrasound than with angiography. (P < 0.0001). An acceptable correlation was found between U-CSA and A-CSA values in normal coronary segments (correlation coefficient: r = 0.73, mean diff. = 1.44 +/- 1.22 mm2). However, the correlation was poor at the site of pre-PTCA lesions (r = 0.62, mean diff. = 1.81 +/- 1.14 mm2) and deteriorated following PTCA (r = 0.47, mean diff. = 1.28 +/- 2.20 mm2). No correlation was found between the degree of lumen eccentricity measured with intracoronary ultrasound (ICUS) and the individual differences between U-CSA and A-CSA values.(ABSTRACT TRUNCATED AT 250 WORDS)