To investigate GH's role in diabetic end organ damage, experimental diabetes was induced with streptozotocin (STZ) in bovine GH (bGH) or bGH antagonist transgenic mice and in their nontransgenic (NTG) litter mates. Body growth, blood glucose, serum insulin-like growth factor-I levels, liver GH receptor (GHR) binding, and kidney histology of these animals were evaluated. After administration of multiple low doses of STZ, 90% of the mice developed hyperglycemia. The diabetic animals, especially those expressing GH and GH antagonist transgenes, demonstrated retarded body growth and reduced insulin-like growth factor-I levels when compared with their nondiabetic litter mates. Kidney histology revealed severe glomerulosclerosis in diabetic and nondiabetic bGH transgenic mice. Diabetic NTG mice exhibited moderate kidney lesions. Diabetic bGH antagonist transgenic mice possessed normal glomeruli indistinguishable from those seen in nondiabetic NTG mice. GHR-binding assays revealed that liver GHR-binding sites were significantly reduced in diabetic NTG mice and transgenic dwarf mice when compared with their nondiabetic controls. Conversely, liver GHR-binding ability was significantly increased in bGH transgenic mice as compared with their NTG littermates and remained high during diabetes. It is concluded that transgenic mice that express a GH antagonist are protected from diabetes and or GH-induced nephropathy.