Scanning electron micrographs were made of the surfaces of silicone rubber finger joint prostheses which had been subjected to 107 bending cycles at 37°C in bovine serum. Preferential attack at the regions of highest stress and the formation of microcracks of length 10μ and less were observed. By way of analogy with the corrosion fatigue phenomenon in metallic alloys, it is suggested that these may be initiation sites for the mechanical failures which have been observed, and that the acceleration of lipid absorption by tensile stress provides potential mechanisms for both initiation and accelerated propagation of fatigue cracks. It is demonstrated as a consequence of mechanochemical thermodynamics that any constituent of the body fluids (e.g. lipids) which can swell the elastomer will in fact be preferentially absorbed at the point of highest tensile stress, i.e., the crack tip, and that swelling will be accelerated by the applications of tensile stress.