Provide holding facilities for large numbers of rats and fewer numbers of mice. Provide standard lab chow diets and prepare the carcinogen-containing and carcinogen-free diets. Determine the subchronic toxicity of specific diets and compounds. Administer the carcinogens, or other agents in the diet, by injection, gavage, skin painting, or implantation. Weigh the animals weekly for the first sixteen weeks of a project and biweekly thereafter. Administer two types of diets: standard lab chow containing carcinogens and other agents; and chemically-defined amino acid diets with and without carcinogens. Unless otherwise specified, all animals will be fed a standard commercial chow diet. House the animals in plastic shoe-box cages and, unless otherwise specified, provide food and water ad libitum.