The interlaminar shear strength of a unidirectional high-modulus polyethylene fibre-epoxy resin composite, measured using a short-beam bend test, increases when the fibre has been plasma treated but decreases with increasing fibre content or increasing filament diameter. Attempts have been made to explain these observations. From observation of the sample failure and the bending load/deflection curves, it was found that there are two possible failure modes dependent on fibre type, fibre volume fraction and fibre plasma treatment. These are (1) brittle failure of the resin and (2) failure at the fibre/resin surface. The present results appear to be consistent with the interlaminar shear strength data obtained from high-modulus polyethylene fibre samples made by the hot compaction process developed at Leeds.