Akt1 is implicated in cell metabolism, survival migration, and gene expression; however, little is known about the role of specific Akt isoforms during inflammation in vivo. Thus, we directly explored the roles of the isoforms Akt1 and Akt2 in acute inflammation models by using mice deficient in either Akt1 or Akt2. Akt1(-/-) mice showed a markedly reduced edema versus Akt2(-/-) and WT controls, and the reduced inflammation was associated with a dramatic decrease in neutrophil and monocyte infiltration. The loss of Akt1 did not affect leukocyte functions in vitro, and bone marrow transplant experiments suggest that host Akt1 regulates leukocyte emigration into inflamed tissues. Moreover, carrageenan-induced edema and the direct propermeability actions of bradykinin and histamine were reduced dramatically in Akt1(-/-) versus WT mice. These findings are supported by in vitro experiments showing that Akt1 deficiency or blockade of nitric oxide synthase markedly reduces histamine-stimulated changes in transendothelial electrical resistance of microvascular endothelial cells. Collectively, these results suggest that Akt1 is necessary for acute inflammation and exerts its actions primarily via regulation of vascular permeability, leading to edema and leukocyte extravasation.