In transgenic mice expression of the transgene occurs primarily in the liver with some expression in other tissues. Addition of 25mM zinc sulfate to drinking water induces maximum expression of the transgene, although expression of the transgene occurs without zinc sulfate stimulation. Serum levels of growth hormone are high but variable. Transgenic mice exhibit a 30-50% increase in body weight, dull coat, and long skeletal bone length. Overexpression of the growth hormone results in liver cancer by one year of age in 70% of transgenic mice. Chronic hepatitis, regenerative hyperplasia, and necroinflammatory changes in the liver precede the development of hepatocellular adenoma and carcinoma. Histological and immunohistological examination reveal liver inflammation develops at 4-5 months of age with prevalent apoptotic hepatocytes and Mallory bodies. By 10 months of age, hepatocellular adenoma develops. Hepatocellular carcinoma, primarily trabecular, develops by 13 months of age. Transgenic mice display a reduction of the natural killer T (NKT) cell number in the intrahepatic lymphocyte population.