This testimony concerned occupationally related cancers. The list of such cancers has continued to grow; a brief review of the known associations between exposures on the job and the occurrence of cancer in the worker was provided. The fact that the latency periods vary to such a great extent, that individual differences are great, and that society is highly mobile, has made it difficult to detect clusters of cancer cases. NIOSH and OSHA were engaged in a study in Texas City where there appeared to be an excess of cases of brain tumors among workers at a Union Carbide facility. Occupational cancer frequently has been found in one organ system with one particular cell type being predominant. Experimental evidence thus far has been unable to show a level of exposure to a carcinogen below which there was not some increased risk of cancer. This has necessitated the government to consider new and more effective ways to encourage and enforce prevention. The issue of substitution of less hazardous materials for other, more hazardous ones, has been considered in many applications. Through the efforts of the National Toxicology Program, the results of cancer research conducted by NIOSH and other agencies has been available to all government regulatory agencies.