When 1,1-dimethylhydrazine and N-aminopiperidine were deliberately exposed to air substantial amounts of the corresponding carcinogenic nitrosamines were formed. Unoxidized samples of 1,1-dimethylhydrazine were not mutagenic while oxidized samples (which contained much higher levels of nitrosamines) were mutagenic. Both unoxidized and oxidized samples of N-aminopiperidine were mutagenic.