The effects of pyridinol carbamate, a drug with demonstrated capacity to inhibit development of atherosclerotic plaques in the rabbit, were studied in humans with symptoms of arterial occlusive disease in the lower extremities. Microcirculation, perfusion, claudication distance, peripheral pulsations, and angiographic appearances were supplemented by clinical impressions over a two-year period. Although the drug was discontinued in several patients from a larger group because of gastrointestinal tract symptoms, and for other reasons, seven of eight patients receiving it showed no progression of their disease, whereas all 15 patients receiving identical-appearing placebos did. Although the number of patients is not sufficient to warrant statistical conclusions, the observations were totally objective and strongly encourage further control of studies.