A key to the prevention of childhood cancer is the control of carcinogens to which children are exposed. The first step in this process is to identify those chemicals that are likely to cause cancer in children. The best way to identify carcinogens, today, is the use of the rodent lifetime cancer test--the bioassay. The test has vocal critics, but is adequately reliable if properly used. Perhaps the major criticism concerns the use of the maximum tolerated dose as the highest dose tested. Critics claim that this dose causes cellular killing. The resultant cellular proliferation "fixes" preexisting mutations that can lead to cancer. This occurs but in a small fraction of the tests, and the high dose is necessary to achieve statistical sensitivity. All human carcinogens have been shown, when properly studied, to be carcinogenic in rodents. Many human carcinogens were first shown to cause cancer in rodent tests. Regulators rarely ban chemicals that have been demonstrated to be carcinogenic. Further, most chemicals in use today have not been properly tested. The potential errors in the rodent cancer test seem small when compared to the errors in the economic projections of the effects of restricting chemicals. Although not perfect, the rodent cancer test, when used properly, can help protect our children, and us, from cancer.