240 patients were admitted to a double-blind study to determine the effect of long-term treatment with platelet-function inhibiting agents on occlusive arterial disease in the lower extremities. Patients were randomised into 1 of 3 treatment groups: aspirin 330 mg; dipyridamole 75 mg and aspirin 330 mg; or matching placebo 3 times daily. The duration of treatment was 2 years. Arteriography was carried out at the beginning of the study and 2 years later or before if deterioration was observed. 199 patients completed the study according to the trial protocol. The serial arteriograms were assessed in pairs qualitatively, by means of simple comparative viewing, and semiquantitatively with Bollinger's score system. Progression of the disease was most pronounced in the placebo-treated group, less so in the aspirin-treated group, and least of all in the dipyridamole-and-aspirin group. Patients who smoke and those with hypertension may benefit most from treatment with the 2 preparations under investigation.