In a double-blind control of xanthinol nicotinate ('Complamin'; 'Complamex') in patients with severe progressive obliterative vascular disease, 25 of 33 patients who completed the trial were helped significantly by the drug, as shown by both clinical and laboratory findings. Placebo helped in 4 of 33 patients. The difference is significant (p less than 0-001). These are the results for the trial period only. The results of follow-up for 6 to 30 months are available in 18 patients: 14 of these still had appreciable help from the drug, which was continued in maintenance doses. It should be noted that 3 of 6 diabetics were no longer helped after 6 months, and that only 3 of a total of 7 patients under the age of 50 were helped; however 3 of the 4 not helped were diabetics under the age of 50. Special caution was indicated in the use of the drug in patients who have ischaemic heart disease in addition to their peripheral arterial disease. Side-effects were common, particularly a severe prolonged flush shortly after taking a dose of the drug; many patients helped by it accepted this side-effect if it occurred. Xanthinol nicotinate reduced whole-blood viscosity and cholesterol and fibrinogen in about half of the patients helped. This is a useful drug for about half the patients in whom surgery is not indicated or is contraindicated.