The efficacy of Trental (pentoxifylline) in the treatment of intermittent claudication was evaluated in 14 double-blind randomized studies, involving 475 patients with chronic occlusive vascular disease. In twelve studies which were performed in the USA, different countries of Europe and Australia, a placebo was used as control. Low doses of adenosine or nylidrine respectively, were given to the control groups in the other two studies. A total of 238 patients were allotted to Trental and 237 to the control groups. In most studies, the recommended dosage of Trental was 3 X 400 mg pentoxifylline in sustained release tablets. Twelve of the 14 trials had a duration between 8 and 24 weeks. The efficacy of Trental was established in a reproducible manner through the trial series under different trial designs following the requirements and guidelines from local authorities and medical societies. The number of patients with an improvement in walking distance of more than 100% was four times higher in the Trental group compared with the control group. The superiority of the Trental treatment over the control's persisted also when taking into account risk factors such as diabetes, hypertension, smoking habits and duration of the disease.