The effect of a new long-acting calcium antagonist, Amlodipine, on experimental vasospasm was tested using arat femoral artery vasospasm model and morphometry. Twenty-four rats were divided into 3 groups. In group I, the femoral arteries were removed after cardiac perfusion. In groups 2 and 3, the right and covered with a silastic cuff. In these groups the left femoral arteries were covered with an empty silastic cuff, Animals in group 3 were treated with Amlodipine (10 mg/kg) for 7 consecutive days. After perfusion-fixation the femoral arteries were examined by light and transsmission electron microscopy and processed for morphometric analysis, Vessels from animals in group 2 showed significant luminal narrowing and morphological changes throughout the vessel wall. In animals treated with Amlodipine, the vessellumen was slightly decreased and light and transmission electron microscopy demonstrated less prominent morphological changes in the vessel wall. These results suggest that Amlodipine can prevent chronic morphological vasospasm in rats.