In order to study kinetics and mechanisms of accelerated repopulation in squamous cell carcinomas, appropriate animal experiments are indispensable. Therefore, over the last 10 years, an extensive experimental programme on various aspects of accelerated repopulation during daily fractionated radiotherapy in isogenic squamous cell carcinomas and in normal squamous epithelium of the oral mucosa of the C3H mouse has been performed. Results of these experiments have been published (Doerr and Kummermehr, 1990, 1991; Trott and Kummermehr, 1991) and together with some recent unpublished data are reanalysed here to derive some information on the mechanisms that lead to acceleration of repopulation during radiotherapy