Akt2 encodes a protein-serine/threonine kinase containing a pleckstrin homology domain characteristic of many signaling molecules. Although there has been extensive interest in the mechanism by which the closely-related Akt kinase participates in phosphatidylinositol 3-kinase-mediated signaling, comparatively little is known regarding the expression and function of Akt2. This manuscript is the first to describe Akt2 mRNA expression in the developing mouse and the activation of AKT2 by insulin. These studies demonstrate that Akt2 is especially abundant in brown fat and, to a lesser extent, skeletal muscle and liver, tissues which are highly insulin-responsive and play a role in glucose metabolism. Endogenous Akt2 expression also is upregulated in fully-differentiated C2C12 myotubes and 3T3-L1 adipocytes, suggesting that these murine cell lines represent useful in vitro models for studies of Akt2 function. We show that HA-tagged AKT2 is activated in response to insulin stimulation in vitro and that activation of AKT2 is not induced in cells pretreated with wortmannin, an inhibitor of phosphatidylinositol 3-kinase. These data suggest that Akt2 expression is fundamental to the differentiated state of fat and muscle cells and that activation of AKT2 kinase by insulin is mediated through the phosphatidylinositol 3-kinase signaling pathway.