Effects of a Behavioral Stimulus on Blood Pressure of Rats with Experimental Pyelonephritis

&NA; Pyelonephritis was produced in rats with E. coli or Proteus mirabilis and the animals exposed to 4 hr. of a paired light‐shock stress for 6–11 weeks. Animals infected with E. coli and receiving the shock demonstrated a higher blood pressure than nonshocked infected rats, but the blood pressure did not rise to hypertensive levels. Prolongation of exposure did not increase the difference. Male rats infected with the Proteus had the most renal destruction and did develop hypertensive levels of blood pressure with shock; female rats who had less severe pyelonephritis with Proteus, did not. Shock, per se, did not significantly aggravate the severity or intensity of the pyelonephritis. It is suggested that the blood pressure change represents an increase in pressor responsivity produced by shock, with the severity of the pyelonephritis determining the intensity of the pressor stimulus.