The lipophilic calcium antagonist Nimodipine (Bayer Pharma , Wuppertal ) was administered during aneurysm operations in 40 patients with ruptured intracranial aneurysm. Immediately after clipping of the aneurysm, a 2.4 X 10(-5) M solution of Nimodipine in 18 ml of Ringer's solution was injected into the subarachnoid space near the site of aneurysm clipping. Arterial vessels regularly dilated and spastic portions resumed their normal diameters. Since it is known from experimental work, that Nimodipine has stronger dilator capacity than papaverine and acts at least for several hours, two conclusions are drawn from the present preliminary study: Pre-operative vasospasm seen on angiograms is no longer a contraindication to early operation because spasm detected intraoperatively can be effectively treated. The long-lasting effect of Nimodipine prevents ischaemic complications in the first few days after operation and thereby seems to exert a protective effect against the onset of severe symptomatic vasospasm.