Hereditary polycystic kidney disease (PKD) was seen in Han:SPRD rats and identified as an autosomal, incomplete dominant trait. Homozygous animals died at 3 to 4 weeks of age, while heterozygous males were severely ill or moribund within about 6 months. Heterozygous females developed PKD to a lesser extent than males and survived longer. Renal secondary hyperparathyroidism and osteodystrophia fibrosa were seen in most males but were absent in females. In male rats metastatic calcification was found in kidneys, lungs, glandular and forestomach, blood vessels, and heart. In a few uremic males ulcerative enteritis occurred in cecum and colon. Blood urea nitrogen values were significantly increased in both sexes.