A subarachnoid haemorrhage (SAH) in the rat was produced by the injection of blood via a previously implanted catheter connected to the cisterna magna. Repeated angiographical examinations of the vertebro-basilar arteries revealed a biphasic vasospasm with a maximal acute spasm at ten minutes and a maximal late spasm at two days after cisternal blood injection. Fluorescence microscopical examination of the major cerebral arteries at day two after the SAH revealed a reduction in the fluorescence intensity and in the number of histochemically visible sympathetic nerve terminals.