A test provocation of coronary artery spasm by alkalosis was used to evaluate a possible anti-coronary artery spasm effect of molsidomine. The rapid infusion of an alkaline buffer followed by maximal voluntary hyperventilation in 10 patients with angina at rest led to the appearance of angina pain and significant, transient ischaemic changes of the ST segment, due to alkalosis induced coronary spasm. A second provocation test was performed under the same conditions, 24 hours later, after the prior administration of 4 mg of molsidomine. Molsidomine prevented the development of coronary artery spasm in 8 of the 10 patients in the study group. These preliminary results justify further clinical evaluation of molsidomine in the treatment of vasospastic angina.