Spontaneously hypertensive rats (SHR) were autopsied at timed intervals from weaning to 28 months. Blood pressure reached 180 to 240 mm Hg after 4 months and was maintained. After 20 months, male SHR began to die of myocardial infarction. A survey was made of the histopathologic changes associated with increasing blood pressure and age. Histopathologic changes appeared in males when they became 8 months old; degenerative changes did not appear in female SHR until 12 to 15 months. Degenerative changes consisted of pituitary basophilia, fatty liver, islet hyperplasia and beta cell degranulation which preceded and became exacerbated with worsening hypertension. Intimal fibrino hyalin lesions of the gonads, polyarteritis nodosa, myocardial infarction, and cerebral edema were more severe in males vs females. Female SHR live significantly longer than males (e.g., 28 to 34 months). Hypertension and longevity may be under separate genetic control in SHR.