3 groups of weanling hamsters were given twice weekly intragastric instillations of NMU at either 20 mg/kg body weight for 5 weeks, 10 mg/kg for 16 weeks or 5 mg/kg for 12 weeks. Cytotoxic effects led to the early loss of 42 out of the group of 54 that received the highest dose but the yield of oral carcinomas in survivors was 83 per cent. Nine of the 14 animals that received 10 mg/kg doses and 3 out of the 9 in the 5 mg/kg group developed oral tumours; in both these experiments, the survival rate exceeded 75 per cent. Longer dosing periods favoured the development of gastric neoplasms. Premalignant oral lesions were found in 81 per cent of the total number of surviving animals. The site distribution of oral lesions was characteristic, with the gingiva, posterior hard palate and lingual dorsum most frequently affected. These findings confirm the value of systemic administration of NMU in experimental oral carcinogenesis.
