Effects of vitamin E and Se on cancer induced by N-N'itroso-N-Methylurea. which is a chemical carcinogen were investigated in this study. The study was carried out with 50 female Wistar-AIbino rats. The animals were divided into five groups: Four experimental and 1 control (n: 10). The animals in groups 1 and II were daily given 3ppm/lt sodium sclcnit via drinking water starting 45 days prior to NMU injection, while groups II and IV were injected vitamin E intraperitoneally (i.p) three times a week. At the end of the 45-day-period blood samples were taken from each animal in individual group via tail veins and the experimental groups (1-4) were administrated 20 mg/kg of NMU intraperitoneally three times a week during the second 45-day-period. After this stage vitamin E and Se application was prolonged for ¡70 days (experimental stage totally lasted for 260 days). All animals were sacrificed at the end of the study after the blood samples were obtained. Histologically, tumourai mass development was obtained in one (10%), five (50%), two (20%) and two animals (20%) in groups I (Se+NMU). II (Se+Vit.E+NMU). Ill (Vit.E+NMU) and IV (NMU), respectively. In conclusion, the ratio of tumourai development in group I. which was slightly lower than in group I pointed out at least the partial effectiveness of Se on prevention of neoplastic development. On the other hand, vitamin E was demonstrated to be ineffective in the prophylaxis of tumourai development due to equal tumour incidences detected in groups III (Vit.E) and IV (Only NMU). The ratio of tumourai development in group II (Se+Vit.E) was detected to be significantly higher than the other groups. Serum Se and vit.E levels in the relevant group were demonstrated to be lower than in group I (despite the insignificance of the estimated value) and significantly higher (p<0.05) than in group III. respectively, which all together indicated the likelihood of the inductive role of high serum levels of vit.E in tumour development.