The diameter changes of angiographically normal coronary arteries following vasodilator drugs were studied in 41 patients. In group 1 (22 patients) angiograms and plasma levels were obtained before as well as 10, 20 and 30 minutes after 20 mg nifedipine s.l. (15 patients) or placebo (7 patients). A cluster analysis allowed a classification of patients into group A (N = 4) and B (N = 11) according to the slope of plasma level increase. Plasma levels A versus B were 27.8 +/- 9.8/13.5 +/- 4.5 ng ml-1; P less than 0.05; 54.0 +/- 11.7/21.7 +/- 6.6 ng ml-1; P less than 0.001; 79.1 +/- 9.3/28 +/- 9.8 ng ml-1; P less than 0.001. Corresponding diameter changes A versus B were: 7.3 +/- 5.1%/-5.6 +/- 9.0%; P less than 0.01; 11.4 +/- 4.1%/-4.5 +/- 11.3%; P less than 0.01; 14.5 +/- 5.9%/0.5 +/- 13.6%; P less than 0.05. In group 2 (N = 19) angiograms were obtained before as well as 2, 4, 7 and 15 minutes after administration of 10 mg isosorbide dinitrate (N = 9) or placebo (N = 10). Coronary dilation ISDN versus placebo was: 2.4 +/- 3.6%/0.9 +/- 4.0%; NS; 10.6 +/- 5.1%/3.1 +/- 3.8%; P less than 0.001; 12.3 +/- 5.9%/-0.3 +/- 6.4%; P less than 0.005; 10.5 +/- 6.5%/-4.0 +/- 7.7%; P less than 0.005. These data indicate that the interindividual variations of changes in coronary lumen size are due to different slopes of plasma level increase, most likely due to different rates of drug absorption after sublingual administration of nifedipine.(ABSTRACT TRUNCATED AT 250 WORDS)