Percutaneous transluminal coronary angioscopy with a flexible steerable microangioscope was performed in five patients undergoing repeat angioplasty. Recurrent lesions were assessed by angioscopy before and after the angioplasty procedure. The most common surface morphology observed in these restenosis lesions was that of white unpigmented lesions consistent with the proliferation of fibrous tissue. Also noted during angioscopy was the presence or absence of thrombus or dissection in association with the lesions either before or after angioplasty. Filmy wisps of tissue, presumably intimal flaps, were commonly visualized after angioplasty. There were no complications related to angioscopy or angioplasty in these patients. The surface morphology of restenosis lesions appears to be different from that of primary atherosclerotic lesions. The lesions in these five patients with restenosis were generally white and fibrotic in appearance, as opposed to the pigmented yellow to yellow-brown lesions commonly seen in undilated atherosclerotic lesions. It was also noted that the presence of intracoronary thrombus was strongly associated with the clinical syndrome of unstable angina. These findings support the hypothesis that restenosis lesions are the result of a reparative process consisting of smooth muscle cell proliferation and fibrosis.