The paper gives results of a study of the possibility that co-firing waste combustors with high-sulfur coal can control the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). In this study , commercial, densified, refuse-derived fuel (dRDF) was co-fired with high-sulfur Illinois No. 6 coal in a 2-million Btu/hr (0.6 MW) stoker combustor. Additional parameters varied in the tests include dRDF feed rate, hydrogen chloride (HCl) concentration, sorbent injection, and flue gas quench rate. Flue gas was sampled for PCDDs and PCDFs from three locations at nominal temperatures of 600, 300, and 150 C. Results also show that coal co-firing inhibits PCDD and PCDF formation substantially. Injection of hydrated lime sorbent is also effective in reducing their formation. Combustion quality, dRDF feed rate, and HCl concentration are some of the other parameters that influence PCDD and PCDF formation.