This testimony before the Subcommittee on Manpower and Housing described the activities of NIOSH in protecting workers from hazards encountered on the job. NIOSH sponsored research was directed to determining what physical and chemical hazards were present at the job site, what adverse effects they produced, and how workers could be best protected from these effects. As many as 100,000 Americans may die each year from occupational diseases. These figures are not as precise as one would desire due to the fact that occupational disease is too often improperly diagnosed and vastly underreported. NIOSH attempts to develop criteria recommending safe exposure levels for toxic substances and harmful physical agents. A priority system was developed and revised to consider new information relating to toxicity or carcinogenicity, new recommendations by professional societies, and toxicity reports for which there is no OSHA standard. A Standards Completion Program was conducted jointly with OSHA to issue more complete standards for the 400 toxic substances currently regulated by OSHA. NIOSH also issues current intelligence bulletins for new information on potentially dangerous chemical substances. Hundreds of other chemicals are studied each year through the conducting of health hazard evaluations, industrywide studies, the National Occupational Hazard Survey, and other research and technical assistance activities. Difficulties encountered in identifying products in trade named items were discussed. Concerns over proprietary information have been important issues.