In 10 patients with coronary artery disease coronary angiograms were performed in identical projections before and 5, 10 and 15 min after sublingual administration of two chewing capsules with 5 mg of isosorbide dinitrate (ISDN) each. Simultaneously, blood samples were taken for gas-chromatographical determination of nitrate plasma levels. The average ISDN plasma levels amounted to 138 +/- 73 ng/ml, 102 +/- 76 ng/ml and 62 +/- 34 ng/ml in the fifth, tenth and fifteenth min, resp. In the fifteenth min significant isosorbide mononitrate plasma levels (greater than 70 ng/ml) were found only in three patients. Mean diameters of angiographically normal coronary segments were measured with the automatic edge detection system CAAS; they increased by an average of 20 +/- 10%, 26 +/- 11%, and 27 +/- 13% (p less than 0.001) in the fifth, tenth and fifteenth min, resp. Due to hysteresis of the coronary dilation in relation to ISDN plasma levels no significant correlation was found between these parameters. The minimal diameters of seven of 10 coronary stenoses analyzed in seven patients reacted with a maximal increase of 23%-98%. Thus, ISDN chewing capsules may be preferable for rapid and prolonged relief of anginal attacks as well as for potent dilation of epicardial coronary arteries as desired during angiography.