The molecular mechanisms responsible for alterations in lysine alpha-ketoglutarate reductase (LKR) activity are unknown. Therefore, the aim of these studies was to discern the mechanism(s) responsible for induction of hepatic LKR activity in rodents fed excess dietary protein. Four studies were conducted that used 84 mice. Mice were fed either a high-protein (50% casein) or adequate-protein (20% casein) diet in powder form in study 1 and a high-protein (46% casein) or adequate-protein (21% casein) diet in pellet form in the remaining studies. No significant differences in weight gain between the mice fed the different diets were detected. As expected, mice fed high-protein diets had a greater (P< .05) LKR activity in all 4 experiments. Mice fed high- and adequate-protein diets for 8 days showed no difference (P> .1) in alpha-aminoadipate delta-semialdehyde synthase (AASS) mRNA in experiment 1. However, after pooling the data from the remaining 3 experiments, mice receiving the high-protein diet had greater (P< .05) AASS mRNA compared to mice fed the adequate protein diet. In this investigation, no differences (P> .1) in AASS protein abundance were detected. The results are consistent with a mechanism in which posttranslational regulation is responsible for hepatic induction of LKR activity in mice fed high-protein diets.