The effect of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) on monoamine neurons was studied in mice and rats. In mice DSP4 produced acutely a marked reduction of endogenous noradrenaline (NA), [3H]NA uptake and nerve density of the adrenergic nerves in the iris and atrium. Pronounced accumulations of NA were observed in non-terminal axons, which is a degenerative sign, while no changes were found in the NA cell bodies. A marked recovery of all parameters analysed was found as soon as 1 week after DSP4. In the mouse CNS, however, there was a marked and long-lasting NA reduction, especially in the cerebral and cerebellar cortex and spinal cord, leaving dopamine (DA) and serotonin (5-HT) neurons apparently unaffected. Administration of DSP4 to adult rats produced regional changes in the NA levels of the CNS were similar to those observed in the mouse. There were no indications of DSP4 affecting dopamine and adrenaline neurons in rat CNS, although a minor 5-HT depleting effect was noted. DSP4 treatment resulted in an increase in beta-adrenoceptor binding in vitro to homogenates from the cerebral cortex, using [3H]dihydroalprenolol as radioligand. Treatment of newborn rats with DSP4 caused permanent NA disappearance in the cerebral cortex and spinal cord, whereas marked NA increases were found in the pons-medulla and cerebellum. Administration of DSP4 to pregnant rats (gestation day 15) led to a marked and permanent NA depletion in the cerebral cortex and spinal cord in the offspring. The results support the view that DSP4 can produce an acute and relatively selective degeneration of NA nerve terminals in the rat and mouse. The results furthermore indicate that DSP4 (systemically administered) causes a preferential degeneration of NA nerve terminal projections originating from the locus coeruleus in the CNS. Since DSP4 can pass both the blood-brain and blood-placenta barrier and appears to have potent neurotoxic actions on NA neurons, DSP4 may serve as a useful denervation tool for the analysis of NA transmitter functions, particularly in the CNS of both adult and developing animals.