Ketanserin, a selective serotonin (5-HT) antagonist at 5-HT2 receptors, was investigated in a 12-month, double-blind placebo-controlled study in 35 patients with intermittent claudication. Benefit was assessed by repeated treadmill tests, recording claudication distance, and by measurement of Doppler ankle-brachial pressure indices (ABPI) and pulse volume recordings (PVR). Improvement in claudication distance of 42-44% was noted during the 12 months of the double-blind study and this trend continued to 53-67% during an additional 3 month run-out period on placebo. There were no significant differences between the group given Ketanserin and the placebo group. The hemodynamic measurements demonstrated no statistically significant change in either ABPI or PVR throughout the study period, and no significant differences between the two groups. The conclusion of the study indicates that Ketanserin is ineffective in the treatment of intermittent claudication.