In vivo tests for a carcinogenic metabolite in plasma of animals given injections of ethyl carbamate (urethan).

Plasma, obtained from rabbits given injections of urethan 2J hours previously, when administered intraperitoneally to Swiss mice, produced a significantly increased inci dence of lung adenomas in these animals, as well as an increased incidence of skin papillomas at the site of subsequent croton oil applications. These effects were not obtained when the plasma was lyophilized or desiccated, with the consequent removal of the free urethan. The condensed vapors collected dur ing the process of lyophilization, on the other hand, were carcinogenic. Carbonyl-labeled urethan-C14 was used to determine the urethan content of the