A new approach for the calculation of relative biological effectiveness (RBE) for normal tissue complications after charged particle and neutron irradiation is discussed. It is based on the extension of a model originally developed for the application to cell survival. It can be shown that according to the model RBE values are determined largely by the alpha/beta-ratio of the photon dose response curve, but are expected to be nearly independent of the absolute values of alpha and beta. Thus the model can be applied to normal tissue complications as well, where alpha/beta- ratios can be determined by means of fractionation experiments. Agreement of model predictions and experimental results obtained in animal experiments confirm the applicability of the model even in the case of complex biological endpoints.