  We consider a delay differential equation that occurs in the study of chronic
myelogenous leukemia. After shortly reminding some previous results concerning
the stability of equilibrium solutions, we concentrate on the study of
stability of periodic solutions emerged by Hopf bifurcation from a certain
equilibrium point. We give the algorithm for approximating a center manifold at
a typical point (in the parameter space) of Hopf bifurcation (and an unstable
manifold in the vicinity of such a point, where such a manifold exists). Then
we find the normal form of the equation restricted to the center manifold, by
computing the first Lyapunov coefficient. The normal form allows us to
establish the stability properties of the periodic solutions occurred by Hopf
bifurcation.
