A metabolic pathway by which L-arginine (L-arg) is converted to the biologically active compound NO. has recently been described in macrophages (M phi) and endothelial cells. This report demonstrates that transferable products from activated Kupffer cells (KC) induce the conversion of large quantities of L-arg to nitrogen oxides within hepatocytes (HC). In M phi and endothelial cells, citrulline and NO2-/NO3- are the stable endproducts of this metabolic pathway. In contrast, HC L-arg metabolism resulted in significantly greater production of NO2-/NO3- than citrulline. The generation of NO. within HC was associated with a concurrent decrease in total protein synthesis.