The effect of combined stimulation of peripheral chemo- and baroreceptors upon sympathetic discharge was studied in cats anesthetized with chloralose and urethan, immobilized with tricuran, and artificially ventilated. The right carotid sinus was arterially isolated, the left sinus nerve and both vago-sympathetic trunks were cut. A rise of pressure in isolated carotid sinus from 100 to 200 mm Hg produced an inhibition of sympathetic activity recorded simultaneously from the inferior cardiac and the renal nerves. For a combined chemo- and baroreceptor stimulation, the carotid sinus was perfused at a constant pressure of 100 mm Hg with venous blood bubbled with CO2.Twenty seconds after the onset of the perfusion the carotid sinus pressure was raised up to 200 mm Hg. A combination of the chemoreceptor stimulation and of the rise of sinus pressure produced only a small inhibition of sympathetic activity in both nerves compared to the effect observed without concomitant chemoreceptor activation. It was demonstrated that chemically induced stimulation of the carotid body chemoreceptors strongly influences the magnitude of the sympathetic inhibition produced by activation of the baroreceptor reflex.