During a 14-day period, 45 of 78 rabbits were treated intravenously with chlorpromazine (5 mg kg-1 day-1). Metrizamide or iohexol was injected subarachnoidally and the neurotoxic effects of each substance on rabbit behaviour were evaluated for 3 h in both chlorpromazine-treated and non-treated rabbits. Chlorpromazine increased both the excitative and the depressive effects of metrizamide and the depressive effects of iohexol. No signs of excitation were observed in chlorpromazine-treated and non-treated rabbits after subarachnoid injections of iohexol. In spite of a free flow of clear fluid from the needle both before and after the intended subarachnoid injection, radiography disclosed that 26 of 67 suboccipital injections inadvertently resulted in a subdural deposition of the contrast medium. Contrast medium effects following subdural injection significantly differed from those following subarachnoid injection.