The association of radiotherapy (RT) and chemotherapy (CT) is clearly beneficial in tumours which are both chemosensitive and radiosensitive (Tubiana et al. 1987). However, contrary to the expectations, in most solid tumours this association did not lead to significant progress in long-term survival. In head and neck cancers, for example, despite a large number of controlled clinical trials, there is not yet a clear-cut demonstration of any increase in survival (DeVita et al. 1986, Tannock and Browman 1986, Taylor 1987, Tubiana et al. 1985). These disappointing results are probably due to two factors: (1) the insufficient effectiveness of the available drugs on most solid tumours; (2) the cumulative toxic effects of radiation and drugs on the normal tissues, which limits the dose of both modalities in combined treatments.