A number of rodent models of prostate carcinoma development have been established to study mechanisms and modifying potential. All except for transgenic mouse models need long experimental periods for generation of a high yield of cancers. Spontaneous prostate tumor models, while not practical in terms of time and tumor incidences, allow the natural course of multistep neoplasia to be followed without a need for chemical exposure. Carcinogens, especially in combination with testosterone, can induce prostate carcinomas in rats, but none are prostate-specific, so that tumor development in other organs is a complicating factor. Induction of invasive prostate carcinomas in the rat frequently requires long-term administration of a pharmacological dose of testosterone with or without application of a chemical carcinogen. While there are several transgenic mouse models, each also has strong and weak points, and it is therefore necessary to select the best model for the purpose of any experimental study.