The effects of clofibrate ('Atromid-S'), 2·0 g. daily, on fibrinolytic activity, platelet stickiness, plasma-fibrinogen, and serum-cholesterol were assessed in eight patients with occlusive vascular disease who were treated for 7 months, and, except for one patient who died, observed for 2 months thereafter. Mean serum-cholesterol was reduced by about 30% and mean plasma-fibrinogen by about 20%. Platelet stickiness was appreciably reduced at first, but after 4-6 months' treatment much of the effect of clofibrate in this respect was lost, the levels returning to the abnormal range. In five of six patients whose fibrinolytic activity was within normal limits before treatment, the dilute blood-clot lysis-times were prolonged whilst clofibrate was given; in two patients prolongation was temporary, but in three it persisted. Hence clofibrate has antifibrinolytic properties, which should be taken into account if the drug is given to patients with coronary-artery disease before the results of controlled trials of its use in this condition become known.