Samples of sewage sludge burned at one fluidized-bed and three multiple-hearth incinerators were subjected to laboratory flow reactor thermal decomposition testing under both pyrolytic and oxidative atmospheres. The laboratory test results indicated that biomass decomposition products, not toxic industrial contaminants, comprised the majority of the emissions. Benzene, toluene, ethylbenzene, acrylonitrile, and acetonitrile were consistently the most environmentally significant products of thermal exposure. Comparison of the results from in the study with those obtained in the field was complicated by an apparent loss of volatile chlorocarbons from the sludge samples received for laboratory testing. However, quantitative comparison of emission factors derived from lab and field results for those compounds observed in both studies showed excellent correlation for the pyrolysis testing.