A structured model of the HPA axis that includes the glucocorticoid receptor (GR) is considered. The model includes nonlinear dynamics of pituitary GR synthesis. The nonlinear eect arises from the fact that GR homodimerizes after cortisol activation and induces its own synthesis in the pituitary. This homodimerization makes possible two stable steady states (low and high) and one unstable state. The model includes also delay on stress. It is shown that concurrence between trajectories of dynamical system, which are produced by the unstable manifold and the value of delay time τ produce slow oscillating asymptotic periodic oscillations of cortisol with a period, which is grater then 2τ. It is shown that such oscillations exist only in an interval τ1 < τ < τ2 , where exact formulas for τ1 and τ2 has been obtained. Such oscillation arise when an initial values of stress are lager of some threshold.