Incineration is currently being used for disposal of about 10% of the solid waste generated in the United States, and this percentage will likely increase as land disposal declines. Siting new incinerators, however, is often controversial because of concerns related to the possibility of adverse health effects and environmental contamination from long-term exposure to stack emissions. Specific concerns relate to the adequacies of a) stack emission testing protocols, b) existing regulations, and c) compliance monitoring and enforcement of regulations. U.S. Environmental Protection Agency laboratories are cooperatively conducting research aimed at developing new testing equipment and procedures that will allow a more comprehensive assessment of the complex mixture of organics that is present in stack emissions. These efforts are directed specifically toward developing source testing equipment and procedures, analytical procedures, and bioassay procedures. The objectives of this study were to field test two types of high-volume source dilution samplers, collect stack samples for use in developing analytical and mutagenicity bioassay procedures, and determine mutagenicity of organics associated with emission particles from two municipal waste combustors and a hospital waste combustor. Data are presented for particle concentrations and emission rates, extractable organic concentrations and emission rates, and Salmonella (Ames) mutagenic potency and emission rates. The mutagenic emission rates and emission factors are compared to other incinerators and combustion sources.