The report gives results of a study to determine the extent of the present onsite use of waste fuel in industrial boilers and related process equipment, the nature and quantities of the materials so disposed of, and current regulations concerning such use. The study responds to a request for comment and advice on recently promulgated hazardous waste regulations that allow the onsite use of wastes as fuels with few restrictions. Based on contacts with federal, state, and local environmental protection officials, industry personnel, and the open literature, the study concludes that: a wide variety of materials have been burned as fuel in standard or appropriately modified combustion equipment; the practice can be expected to expand due to the economic pressures of hazardous waste disposal and rising fossil fuel costs; virtually no emission data on waste fuel combustion (except through incineration) is available; under conditions of inefficient combustion, significant particulate matter and high molecular weight (including polycyclic organic compounds) emission rates can be expected; and, within the scope of this study, no current regulations were found to be directed specifically at waste combustion. The study recommends increased industry contacts, representative site selection, and a field program in conjunction with a coordinated regulatory program.