Five nitrosamines, which can be considered alkyl derivatives ofN-nitrosodiethylamine, were tested for carcinogenicity by administration to Sprague-Dawley rats in drinking water at approximately equimolar concentrations.N-Nitrosodi-n-propylamine was a potent carcinogen but less so thanN-nitrosodiethylamine and gave the same spectrum of tumors.N-Nitrosodiisopropylamine was very much weaker thanN-nitrosodiethylamine and induced only tumors of the nasal turbinates in significant incidence. At the doses given, neitherN-nitrosodiisobutylamine norN-nitrosodi-sec-butylamine was significantly carcinogenic. In contrast, the cyclic nitrosamineN-nitrosohexamethyleneimine was equally potent withN-nitrosodiethylamine and gave the same spectrum of tumors in liver, esophagus, and nasal turbinates. The results support the concept that oxidation at the alpha carbon atom of nitrosamines is a significant step in carcinogenesis.