The combined carcinogenic effect of cigarette smoke condensate and urethan.

The role of tobacco tar in the development of lung adenomas was investigated in A mice of both sexes given a single intraperitoneal threshold or subthreshold dose of ethyl carbamate. Incidence of lung tumors indicated a highly significant increase in response to urethan from subthreshold to D50. When additional groups of mice were given urethan and the oral area was painted 5 times weekly for 6 months with a brush full of cigarette-tar solution, the adenoma incidence in groups of mice receiving nrc than plus tobacco condensate was greater for each urethan dose than for the corre sponding group receiving urethan alone. The difference in tumor incidence between the tar-added and urethan-alone groups is highly significant (P < 0.0001). All tumors were alveolar. Furthermore, the addition of tar produced significantly greater than additive effects in terms of incidence. The addition of tar produced effects as though the urethan dose had been increased by a factor of 5@.