[Lower urethane carcinogenicity for the lungs of thymus-free nude mice in comparison with immunologically normal littermate mice].

Lung adenomas arose in 2 of 10 nude mice injected twice with urethane in a dose of 1 mg/g of body weight; these tumours were revealed in 7 of 10 immunologically normal littermates treated in the same way. Mean adenoma numbers were 0.2 +/- 0.13 per nude mouse and 1.2 +/- 0.36 per normal mouse (P less than 0.05). The data obtained do not agree with the immunological surveillance concept which predicts greated number of tumours in the nude mice in comparison with the normal ones.