The effects of excess salt ingestion or/and a prolonged electrical stimulation of the hypothalamus on the arterial blood pressure were studied in cats. The average mean arterial pressure determined in 12 control animals were 112.2±2.6 mmHg. In 15 animals in which 2% NaCl solution (2g/Kg of body wegight/day) was given for 20 days, average mean arterial pressure elevated to 147.7±6.1 mmHg. It was also found in four of them that salt-induced high blood pressure started to decline when salt solution was replaced by tap water. On the other hand, No change in average mean arterial pressure was observed in 10 animals, whose hypothalamus had been electrically stimulated for 28 days. In 11 animals in which the hypothalamus was stimulated with simultaneous excess salt ingestion for 20 days, there was a marked elevation in average mean arterial pressure which, however, does not significantly differ from that observed in excess salt ingested group. From the results obtained from the present experiment, it is concluded that 1) the hypertension is induced by an excess salt ingestion in cats, 2) the mean arterial pressure of cats is not affected at least by an increment of sympathetic tone for 4 weeks resulting from the electrical stimulation of posterior area of the hypothalamus, 3) in sodium¡¤induced high blood pressure cats, four weeks of increment in sympathetic tone by the hypothalamic stimulation does not further elevate mean arterial pressure.