SummaryThis paper is concerned with some versions of a stochastic model of aging proposed recently by TYUXIN et al. (1993). In contrast to the commonly used Gompertz-Makeham approach, the model yields a bounded hazard rate, thereby providing a better description of survival of old individuals in a population. Depending on plausible biological assumptions to be tested, only a few special cases of the basic model appear to be useful in experimental data analysis. We report the results of their application to experimental data on animal longevity obtained in a follow-up study. When interpreted in terms of the model parameters, the data suggest drastically dissimilar patterns of aging for female versus male rats.