n-butyl chloride, benzyl chloride, and l-chloromethylnaph thalene to mice resulted in no significant increase in the frequency of lung tumors over that seen in vehicle-treated control mice. n-Butyl bromide and tert-butyl iodide simi

The production of lung adenomas in strain A mice following multiple injections of 17 alkyl halides and of 3 base analogs was investigated. A slight but significant increase in the average number of lung tumors per mouse was noted following the administration of methyl iodide, n and i-propyl iodide, secand tert-butyl chloride, i-, sec-, and tert-butyl bromide, and nand sec-butyl iodide. The admin istration of comparable doses of ethyl bromide, ethyl iodide, n-butyl chloride, benzyl chloride, and l-chloromethylnaph thalene to mice resulted in no significant increase in the frequency of lung tumors over that seen in vehicle-treated control mice. n-Butyl bromide and tert-butyl iodide simi larly appeared to have no significant effect on the lung tumor frequency, but these compounds were too toxic to be tested at the high dosages used with the other alkyl halides. 5-Iodo-, 5-bromo-, and 5-fluorodeoxyuridine also appeared to have no significant effect on the lung tumor frequency. These results indicate that a high proportion of low-molecu lar-weight alkyl halides may be weakly carcinogenic and provide evidence supporting an electrophilic hypothesis of carcinogenesis.