AbstractA retrospective study of late effects of irradiation on skin and underlying connective tissues in 94 testis tumour patients was conducted 5–8 years after irradiation. The late lesions were classified into five degrees of “severity of injury”. Among this population of patients, there was marked variation of “severity of injury” produced by similar dosage; or when viewed differently, each degree of “severity of injury” was produced by a wide range of doses. Therefore, since the late response of connective tissues was not constant, a “tolerance dose” could not be established, but only a “percent probability of threat” of a specific degree of injury.The data also indicate that within certain limits, the late effects are independent of overall time; and that they are dependent on the size of the daily fraction. Furthermore, biological features of non-proliferating connective tissue are not applicable to dynamically proliferating normal epithelial and cancerous tissues.