The tensile strength, sigma, of biaxially oriented polyethylene (PE) films with various degrees of biaxial stretching has been measured. The dependence of a in the two principal directions x and y is investigated as a function of two parameters: the biaxial draw ratio (average draw ratio of the film) and the degree of biaxiality (strain distribution along the principal directions). Both parameters are related to the final applied pressure P-F. The influence of initial orientation and anisometry of the injection molded precursors on the final sigma(x) and sigma(y) values along the principal directions is studied. Results are discussed in the light of the deformation mechanism which transforms the original uniaxial fiber structure of the moldings into the biaxial fibrillar structure of the final films. Direct evidence of this transformation is provided by small angle X-ray scattering (SAXS).