In baroreceptor denervated cats one internal carotid artery (ICA) or the cerebral ventricular system (CVS) was perfused with isotonic, hypertonic and hypotonic sodium chloride solutions. Renal sympathetic activity (RSA) and blood pressure (BP) were recorded. ICA perfusion with isotonic sodium chloride (150 mM NaCl) produced no changes of RSA compared to control level,. RSA was increased from plus 30% to plus 350% in 44 tests out of 45 tests following hypertonic (425 mM NaCl) ICA perfusion. RSA was decreased following hypotonic (aqua dest.) ICA perfusion from minus 30% to minus 100% in 37 tests out of 50 tests. The degree of RSA changes was found to depend upon the osmolarity of the solutions. 425mM NaCl and aqua dest. produced greater RSA changes than 290 mM NaCl and 75 mM NaCl. CVS perfusion with isotonic sodium chloride produced a slight increase of RSA compared to control levels (plus 15%). Hypertonic sodium chloride produced a RSA increase from plus 15% to plus 135% in 10 tests out of 14 tests. Hypotonic sodium chloride produced a RSA decrease from minus 15% to minus 80% in 8 tests out of 14 tests. Changes of RSA following ICA perfusions and CVS perfusions were accompanied by changes of BP in the same direction. A quantitative correlation between delta RSA and delta BP could not be found. Results suggest that renal osmoregulatory response to osmotic stimuli in the carotid artery may not just arise in response to changing ADH levels but may also be induced by changes in RSA.