In the present work the effects of a 55-day oral treatment with two beta-blocking agents (propranolol 40 mg/kg per day and S 2395 20 mg/kg per day) on the catecholamine (CA) content of central and peripheral structures were studied in spontaneously hypertensive rats (SHR). The concentrations of dopamine (DA), noradrenaline (NA) and adrenaline (A) in different structures dissected out from treated and control SHR were measured by a radioenzymatic method. At the peripheral level, no change in the concentration of NA (in the heart) or A (in the adrenal medulla) was observed. Propranolol increased the DA concentration in the C1 and C2 regions of the medulla oblongata and S 2395 increased the DA concentration only in the C2 region. In these two areas, the NA and A levels were unchanged. Both propranolol and S 2395 increased the DA, NA and A content in the locus coeruleus and in the anterior hypothalamus. On the contrary, there was no modification in the posterior hypothalamus. The anatomical specificity of these alterations of the CA levels suggests that they could be related to a specific action of beta-blockers on central catecholaminergic structures in SHR which might be linked to the antihypertensive effects of these drugs.