Models to calculate the stiffness matrix of a unidirectional composite involve often the use of a concentric cylinder as unit cell. In this paper, an existing concentric cylinder model of Pagano&Tandon has been extended, by applying the Mori-Tanaka and generalised self-consistent scheme theories to this basic model. The aim is to improve the stiffness prediction for three phase composite systems. It will also be pointed out that, although improvements in stiffness prediction can be achieved, the use of these concentric cylinder models for local stress state analysis in polymer matrix composites is rather questionable.