Activation of the mammalian mitogen-activated protein kinase known as BMK1 is required for growth factor-induced cell proliferation. To understand the mechanism by which BMK1 mediates this cellular response, this kinase was used as bait in a yeast two-hybrid-based library screening. Here, we report the identification of serum and glucocorticoid-inducible kinase (SGK) as a cellular protein that physically interacts with BMK1. During growth factor-induced cell stimulation, BMK1 activates SGK by phosphorylation at serine 78. This BMK1-mediated phosphorylation event is necessary for the activation of SGK and, more importantly, for cell proliferation induced by growth factors.