Hypertension was induced in rats (Hebrew University strain) by three different procedures: (1) deoxycorticosterone acetate (DOCA)--salt treatment; (2) unilateral renal artery clip or (3) chronic salt-loading. Noradrenaline (NA) and dopamine (DA) distribution in different brain areas was assayed following induction of hypertension. NA content increased significantly in various areas: the increase of NA in the pons-medulla was common to all procedures inducing hypertension. NA content increased also in the mesencephalon, the hypothalamus and the rest of the forebrain (DOCA--salt hypertension), in the mesencephalon, the hypothalamus and the cortex (in renal clip hypertension). No significant changes in DA content were observed in any region of the brain following induction of hypertension by the three different methods. In two substrains, selected from the Hebrew University strain, for their respective sensitivity (H) or immunity (N) to hypertension induced by DOCA--salt treatment, there were no significant increases in NA or DA in any part of the brain following DOCA--salt treatment. Comparison of NA concentrations in these strains showed that NA was significantly higher in the pons-medulla of the untreated N strain rats than in the medulla of untreated H strain or in untreated rats of the original strain (Hebrew University). A model is presented suggesting that central NA-containing neurons plays a major role in controlling hypertension.