MIF (macrophage migration inhibitory factor) was one of the first cytokine activities to be discovered and was initially described as a T cell-derived factor that inhibits the random migration of microphages. Recently, MIF was rediscovered as a pituitary hormone that acts as the counter-regulatory hormone for glucocorticoid action within the immune system. MIF was released from macrophages and T-cells in response to physiological concentrations of glucocorticoids. The secreted MIF counter-regulates the immunosuppressive effects of steroids on immune cell activation and cytokine production. MIF also plays a critical role in the host control of inflammation and immunity.