The work discussed outlines the development of a technique to predict failure of rubber components under repeated complex stressing. A fracture mechanics approach is adopted, which has been shown to work with simple plane stress type geometry in the past. Real components with three dimensional loading and geometry can be examined with the use of finite element analysis techniques. These now allow us to investigate real fracture type problems to large strain deformations. To predict fatigue behaviour in components it is necessary to derive the energy release rate for that particular component, which in general involves FEA techniques. Also it is important to know the crack growth characteristics of the material. This is usually expressed in terms of the rate of crack growth as a function of the tearing energy (energy release rate). Conventional tearing energy, crack growth tests are performed in relatively simple deformation modes, using for example edge crack or pure shear test pieces. In practice, components used in engineering undergo more complicated strain histories. In order to study these potential complexities in the crack growth characteristics, the effect of pre-strain on cyclic crack growth behaviour using a predominantly pure shear test piece with an applied pre-strain has been studied. For the filled compounds studied so far there do appear to be complications and the observed crack growth rates may be substantially increased by these pre-strains. Some of these results are presented and their consequences discussed.