Recent developments in the application of the two-mutation model of carcinogenesis to the analysis of radiation epidemiologic and animal studies have suggested differing approaches and different insights into the action of radiation. A BEIR VII committee should critically examine the status of models that might be relevant to risk assessment. Multistage models might provide a tool that can be used to relate the molecular investigations on radiation mechanisms at the cellular level to the epidemiologic studies of exposed populations. The models also might provide a basis for extrapolating radiation effects to low doses and low dose rates and across populations which could be useful and meaningful for risk assessment. It must always be borne in mind that any model is a simple representation of the facts and, while the use of the two-mutation model of carcinogenesis might suggest different insights into the action of radiation, considerable care must be taken in applying such models to experimental data and in interpreting the results of such analyses.