The hypertensive inbred mouse strain, BPH/2, has high blood pressure early in life, compared with its hypotensive BPL/1 and normotensive BPN/3 controls. At 21 weeks of age, the hypertensive mouse has a systolic blood pressure 60 mm Hg higher than that of the hypotensive mouse. The difference in blood pressure between hypertensive and hypotensive mice is associated with strain differences in heart rate, heart weight, relative heart weight, left ventricular mass, kidney weight, and hematocrit. These strains have been inbred by brother x sister matings for nearly 50 generations in the BPH/2 and BPL/1 strains, and for nearly 40 generations in the BPN/3 strain.