Experimental studies suggest the primary role of free radical products in the development of vasospasm. In the present study, the iron chelator deferoxamine was used at the time of subarachnoid hemorrhage to prevent chronic cerebral vasospasm. Cats were anesthetized to obtain a baseline digital subtraction angiography of cerebral arteries. Arterial blood was injected into the cisterna magna of all cats. Group 1 (15 cats) received deferoxamine solution intrathecally, and the other 15 were kept as a group 2. Two days later a second angiography was performed that revealed vasospasm in group 2 but no vasospasm in group 1 and the control group. A significant increase in the level of lipid peroxides was found in group 2 as compared with the others in the brain samples. These results suggest that deferoxamine can prevent vasospasm.