The results of five major testing programs of the U.S. EPA's Cincinnati-based Risk Reduction Engineering Laboratory (RREL) are described. Three of the five programs were carried out at RREL's Incineration Research Facility (IRF), a fully-permitted pilot plant operation located in Jefferson, Arkansas. The fourth program was conducted at a full-scale boiler site in Williamsport, Pennsylvania, while the fifth series of tests were done on the 'mini-plot' scale in Kansas City, Missouri. All five testing programs featured various aspects of the thermal destruction of hazardous wastes: soil decontamination; evaluating the recently-developed EPA/RREL Incinerability Ranking Index; partitioning during incineration; investigating the 'hysteresis' phenomenon associated with boilers; and simulated solar destruction.