A double-blind, randomized, placebo-controlled long-term clinical study of Trental 400 was carried out, partly under cross-over design, partly as a parallel-group study, in 36 patients suffering from chronic arterial obstructive disorders in the lower limbs, associated with intermittent claudication, in order to evaluate the effectiveness and the safety of this drug administered t.i.d. over a period of 6 months. This controlled period was preceded by a placebo run-in period of 3 months. The clinical results under Trental 400 showed a statistically significant within group improvement of painfree and maximum walking parameters (p less than 0.05) corresponding to an increase to baseline by +96% to +139% respectively and also in comparison to placebo (p less than 0.05). The alterations of walking parameters within the placebo groups, ranging between -25% and +28% were not significant. The subjective parameters (rest pain, paraesthesias, muscular cramps and sensation of heaviness in the legs) paralleled the course of the walking parameters. Under Trental 400, 24 out of 36 patients reported an improvement of these symptoms compared to 7 under placebo. Trental 400 was well tolerated. Minor side effects were mentioned by 7 out of 36 patients. One patient had to stop the drug treatment because of persisting prickling sensation and subsequent insomnia. Drug-related changes in the laboratory findings could not be detected; vital signs varied in function of age, concomitant drug treatments and seasonal factors. The results obtained in these studies suggest Trental 400 as a drug of choice for treating patients with intermittent claudication due to peripheral arterial obstruction according to stage II or III after Fontaine.