The responses of the noradrenaline (NA)- and adrenaline (A)-containing neurons to a reserpine treatment have been studied in the rat brain by using biochemical indices of the neuronal activity. Three days after multiple reserpine injections, tyrosine hydroxylase activity was significantly increased in the locus coeruleus (LC), A1-C1 and C2 regions. No change in this activity was observed in the A2 region. Furthermore, the NA and A endogenous levels were markedly reduced both in NA and A cell bodies and/or terminals, suggesting a reserpine action on NA and A neurons. The NA turnover was unchanged in all the regions analyzed. Conversely, the A turnover was reduced in the LC, A2 and C2 regions and in the nucleus periventricularis of the hypothalamus. This result suggests a different degree of sensitivity and/or response of the NA and A neurons following reserpine administration.