Compared with pathologic studies coronary angiography is a relatively insensitive technique to detect early atherosclerosis. Coronary angioscopy is a new technique providing direct information on luminal vessel surface. To determine whether coronary angioscopy may detect the presence of atherosclerotic disease on angiographically normal coronary segments, 52 patients underwent a study with coronary angioscopy before coronary angioplasty. The mean age was 59 +/- 10 years; 46 patients were men and 6 were women. The reason for coronary angioplasty was unstable angina in 36 patients, stable angina in 8 patients, and silent ischemia in 8 patients. In seven patients angiography revealed luminal irregularities on the coronary segment proximal to the culprit lesion, and all these patients also had proximal disease as demonstrated by coronary angioscopy. In the remaining 45 (87%) patients angiography revealed a smooth-vessel contour proximal to the target lesion. On quantitative angiography these "normal" coronary segments measured 2.8 +/- 0.4 mm in luminal diameter. In 30 (67%) of these patients angioscopy revealed proximal disease on the vessel wall, but in 15 (33%) patients the luminal surface of these segments also appeared normal on angioscopy. Disease as detected by angioscopy in angiographically normal segments included yellow plaque in 19 patients, mural thrombus in 5, mixed plaques in 4, and small flaps in 2 patients. In eight patients coronary angioscopy detected that atherosclerotic disease extended proximally from the target lesion, but in the remaining 22 patients the angioscopic findings appeared to be discrete and well separated from the angiographic lesion. All these plaques were relatively small and did not protrude into the coronary lumen.(ABSTRACT TRUNCATED AT 250 WORDS)