Intracarotid artery (ica) BCNU was given at doses of 1-20 mg/kg/week for 4 weeks in six rhesus monkeys. Vascular, neurologic, and ophthalmic toxic effects were minor. The monkey receiving a dose of 15 mg/kg had transient left hemiparesis and slowing in her electroencephalogram which cleared 1 week after the third ica infusion of BCNU. At autopsy no vascular, neural, or ophthalmic lesions were found. At doses of 20 mg/kg for two injections, one monkey developed fatty metamorphosis of the liver and Alzheimer II glia in the brain, yet did not develop arteriolitis, corneal damage, or neurologic deficit. It is concluded that reasonable doses of BCNU (less than the systemic maximum tolerated dose) should be well tolerated by ica administration in man.