Radiotherapic treatment of patients with carcinoma usually causes genotoxis damage. This has been studied recently using the test of micronuclei in esfoliated cells. This test presents methodologic advantages in compared with the classic citogenetic analysis and as it is carried out on esfolieted cells from the oral cavity it faithfully reflects the genotoxic damage undergone by the cells of the basal layer of the epitelium. The preliminary result obtained so far have confirmed the anticlastogenic activity of beta-carotene in fact, the frequence of micronuclei in esfolieted cells from the oral cavity in patients undergoing radiotherapy or undergoing treatment with beta-carotene is inferior to that of patients undergoing treatment with beta-carotene is inferior to that of patients undergoing radiotherapy without the subministration of carotenoids. Treatment with carotenoids does not influence the therapeutic efficiency of radiotherapy treatment. Therefore, the results seem to confirm that indirect ossidaction processes are involved in the mechanism of the clastogenic action of radiotherapia. The carotenoids seem to be able to contrast validly this undesirable effect without interfering with the desirable therapeutic effect.