SummaryComparative studies with Syrian Golden and Chinese hamsters after intragastric and subcutaneous treatment with dibutylnitrosamine are reported. In both species morphologically similar tumors of the urinary bladder, forestomach, oral, and nasal cavities occurred. Syrian Golden hamsters mainly had tumors of the lower respiratory tract, while the Chinese hamsters developed tumors mainly of the digestive tract. The effect in each case was not dependent on the route of administration.