We have reported that short-term treatment of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats with stannous chloride (SnCl2), which selectively depletes renal cytochrome P450, restores blood pressure to normal in young but not in adult SHR, and is without effect on blood pressure of either young or adult WKY rats. We report in the present study that chronic treatment with SnCl2, begun at age 5 weeks, prevented the development of hypertension in SHR over a period of 15 weeks at which time they were killed. Suspension of SnCl2 treatment after 8 weeks (i.e., at age 13 weeks) did not result in return of blood pressure to hypertensive levels in SHR. Age-matched WKY rats were not affected by tin treatment. These findings provide additional evidence that administration of tin, which stimulates heme oxygenase, thereby producing depletion of cytochrome P450, restores blood pressure to normal levels in SHR.