The subcutaneous injection of mast cell degranulators in the mouse is followed by calcification of fibres of the Panniculus Carnosus muscle. This reaction is seen in damaged fibres adjacent to a central zone of complete necrosis. Calcification of muscle fibres is also seen after the injection of KMnO4 but this uniformly affects the fibres at the site of reaction. Quantitative studies of the latter model and qualitative studies of the former show that treatments with the diphosphonates EHDP and Cl2MDP do not influence the calcific responses. It is suggested that the inducing chemicals interact with the muscle fibre membrane causing membrane dysfunction and a resultant influx of calcium ions. It has been proposed that this is a pathogenetic mechanism in various myopathies and that prevention of net calcium ion influx might form a basis for treatment. In this context, the results of the present experiments suggest that the diphosphonates would be unlikely to efficacious in this regard.