The article discusses monitoring the waste destruction efficiency of hazardous waste incinerators, to ensure that incinerators do not release, without detection, significant quantities of waste as a result of operating fluctuations or equipment degration. To detect these conditions, continuous, automated, and real-time source monitoring is required. Detection of degraded performance by monitoring and measuring waste compounds directly is not presently possible on a continuous basis. An alternative is to use commercially available continuous monitors to measure combustion intermediates (e.g., CO or hydrocarbons) and thereby infer waste destruction efficiency. Required, however, is a correlation between the emission of intermediates and the emission of waste. The paper compares the response of a number of these continuous monitors with waste destruction efficiency measurements from a laboratory-scale liquid-spray incinerator operated on fuel oil doped with model waste compounds (benzene, chlorobenzene, acrylonitrile, and chloroform).