The effect of various factors on the development of urinary bladder tumor in rats, guinea pigs, and hamsters given N-butyl-N-(4-hydroxybutyl)nitrosoamine was examined histologically. The effect of sex and age, and of the dose and period of administration of N-butyl-N-(4-hydroxybutyl)nitrosoamine on the incidence of urinary bladder tumors in rats was also investigated. No sex difference was found in the incidence of urinary bladder cancer in rats. However, the incidence of cancer and of squamous

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... metaplasia in areas of cancerous tissues was greatly influenced by the age of animals, being much higher in older rats than in younger rats. For development of urinary bladder cancer in rats, the minimum carcinogenic dose of N-butyl-N-(4-hydroxybutyl)nitrosoamine given in the drinking water is 0.005% while 0.001% is the maximum non-carcinogenic dose. On administration of 0.1% carcinogen solution to rats, the minimum period for the induction of urinary bladder cancer is 4 weeks. Guinea pigs and hamsters were less susceptible than Wistar strain rats to the induction of urinary bladder cancer by N-butyl-N-(4-hydroxybutyl)nitrosoamine.