[en] In connection with a wide use of combined action of irradiation and chemotherapy in the treatment of tumours, action of chemicals on the body subjected to irradiation has been studied. Experiments were carried out on white non-bred male rats. Cyclophosphane was administered to animals after 1,4,6 months after a single irradiation at the dose of 400 rad (dose rate 50 rad/min). Results of the experiments show that in the irradiated animals administration of cyclophosphane produces not only a great number of cells with chromosome disorders, but also the increase in the severity of such disorders