We report quantification of vasospasm following subarachnoid haemorrhage (SAH) and the effect of a new antivasospastic free radical scavenger (AVS) in rats, using an angiographic technique developed in our laboratory. We acquired single-exposure angiograms with mammographic equipment, using a 0.1 mm diameter focal spot and single-emulsion mammographic films. Contrast medium was injected through a PE50 catheter in the common carotid artery, after the external carotid artery had been ligated to divert flow towards the internal carotid artery territory. Measurements of the M1 and A1 segments and of the middle third of the basilar artery were made by projecting the angiograms directly as slides and using the endovascular catheter as an internal reference. We tested the technique on 40 male albino Sprague-Dawley rats divided into four groups: sham-operated+saline, SAH+saline, sham-operated+AVS and SAH+AVS. We were able to measure the diameter of the principal intracranial arteries in all the animals. With our technique, which is cost-effective when compared to many of those reported recently, we could detect intracranial vasospasm in all untreated rats with SAH, and confirm antivasospastic effects of AVS.