The present invention provides a method for preferentially reducing the proliferation of cystic epithelial cells in the kidney or bile duct in a mammal in need thereof by administering a 20-HETE synthesizing enzyme inhibitor or a 20-HETE antagonist to the mammal in an amount sufficient to preferentially reduce the proliferation of cystic epithelial cells over normal epithelial cells such as tubule epithelial cells in the kidney or bile duct. The present invention also provides a method for preventing or treating autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), ARPKD associated congenital hepatic fibrosis, ARPKD associated Caroli's disease, or cholangiocarcinoma in a mammal in need thereof by administering a 20-HETE synthesizing enzyme inhibitor or a 20-HETE antagonist to the mammal in an amount sufficient to prevent or treat the disease.