Akt/protein kinase B (PKB) is a serine/threonine kinase which is implicated in mediating a variety of biological responses including cell growth, proliferation and survival. Akt is activated by phosphorylation on two critical residues, namely threonine 308 (Thr308) and serine 473 (Ser473). Several studies have found Akt2 to be amplified or overexpressed at the mRNA level in various tumor cell lines and in a number of human malignancies such as colon, pancreatic and breast cancers. Nevertheless, activation of Akt isoforms by phosphorylation appears to be more clinically significant than Akt2 amplification or overexpression. Many studies in the past 4-5 years have revealed a prognostic and/or predictive role of Akt phosphorylation in breast, prostate and non-small cell lung cancer. Several publications suggest a role of phosphorylated Akt also in endometrial, pancreatic, gastric, tongue and renal cancer. However, different types of assays were used in these studies. Before assessment of P-Akt can be incorporated into routine clinical practice, all aspects of the assay methodology will have to be standardized.