The metabolic fate of N-alkyl-N-(3-hydroxypropyl)nitrosamines and N-alkyl-N-(2-hydroxyethyl)nitrosamines (alkyl=butyl, ethyl) [analogs of N-alkyl-N-(4-hydroxybutyl)nitrosamines, which are potent bladder carcinogens] was investigated in the rat in order to elucidate a possible relationship between chemical structure, in vivo metabolism, and organotropic carcinogenicity to the urinary bladder of N-alkyl-N-(4-hydroxybutyl)nitrosamines. The principal urinary metabolites of N-alkyl-N-(3-hydroxypropyl)nitrosamines and N-alkyl-N-(2-hydroxyethyl)nitrosamines, which are not carcinogenic to the urinary bladder but are hepato-carcinogenic in rats, were the corresponding 2-carboxyethyl and carboxymethyl compounds. Urinary metabolites with a 2-carboxyethyl or carboxymethyl group are not important, as far as the induction of bladder cancer is concerned, and the urinary excretion of metabolites having a 3-carboxypropyl chain is essential for the induction of bladder cancer.