Urinary kallikrein was similar in 16-week-old Wistar/Kyoto (W/Ky) and spontaneously hypertensive (SH) rats, but at 23 weeks the SH rats excreted significantly less kallikrein. When dietary sodium was restricted, kallikrein excretion increased in the W/Ky but not in the SH rats. On high dietary sodium the opposite occurred: kallidrein excretion increased in the SH but not in the W/Ky rats. The pattern of urinary kallikrein excretion has some similarity to that seen in human hypertensive disease, i.e., the SH rat excretes less kallikrein than the normotensive control at 23 weeks of age and does not show an increased excretion when fed a low sodium diet. However, the rise in kallikrein shown by the SH rat on a high sodium diet is unique for this hypertensive model.