The effect of crack bridging reinforcing members on the growth of a transverse fatigue crack in an aluminium alloy sheet has been examined. The specimens have been subjected to zero tension cyclic loading applied in the reinforcement direction. In the case of some specimens initial tensile stresses were developed in the substrate aluminium sheet by the reinforcing members. In other cases initial compressive stresses were developed. Fatigue crack growth rates in the unreinforced aluminium alloy sheet were also determined. In the case of both types of reinforced structures the reinforcing elements suppressed the growth of fatigue cracks compared with the unreinforced material. This effect was particularly marked in the case where the substrate aluminium sheet was prestressed in compression-the crack growth rates approaching zero as the peak applied tensile strain approached the value of the initial compressive pre strain.