Bonfield and Grynpas have compared their experimental data for Young's modulus of elasticity versus the angle of orientation of the specimen to the long axis of bone with a theoretical curve predicted from a calculation for fibre reinforced materials proposed by Currey. As a result of the poor agreement between the two curves they conclude "... an alternative model is required to account for the dependence of Young's modulus on orientation" (ref. 1). Such an alternative has been under development in my laboratory for the past 8 years (refs 3--7). It is a two-level hierarchical fibre-reinforced composite model which appears to provide a much more suitable description of the behaviour of bone as a fibre-reinforced composite material.