Capillaries of quadriceps muscle from a 42-year-old patient with myocardial disease, probably due to alcoholism and/or thiamine deficiency, were studied by electron microscopy. Severe degenerative changes in the capillary walls were demonstrated: the basal lamina was found to be nearly three times as thick as that of normal controls. Furthermore, the basal lamina was frequently found to be duplicated and laminated; the electron-lucent spaces between the lamellae were filled with destroyed pericytes, a variety of cellular debris, undefined granular material, and isolated collagen fibrils. Occasionally, redundant basal lamina curls as well as empty basal lamina cylinders, probably remnants of capillaries, were found situated in the muscular interstitium.