[en] Workers in nuclear weapons facilities have a significant potential for exposure to chemical carcinogens and to radiation from external sources or from internally deposited radionuclides such as ²³⁹Pu. Although the carcinogenic effects of inhaled ²³⁹Pu and many chemicals have been studied individually, very little information is available on their combined effects. One chemical carcinogen that workers could be exposed to via tobacco smoke is the tobacco-specific nitrosamine 4-(N-methyl-n-nitrosamino)-1-(3-pyridyl)-1(3-pyridyl)-1-butanone (NNK), a product of tobacco curing and the pyrolysis of nicotine in tobacco. NNK causes lung tumors in rats, regardless of the route of administration and to a lesser extent liver, nasal, and pancreatic tumors. From the results presented, it can be concluded that exposure to a chemical carcinogen (NNK) in combination with α-particle radiation from inhaled ²³⁹PuO₂ acts in, at best, an additive manner in inducing lung cancer in rats