The report discusses tests, conducted at the U.S. Environmental Protection Agency (EPA) Air Pollution Prevention and Control Division, to evaluate the effects of changing coals on emissions of metal hazardous air pollutants from coal-fired boilers. Six coals were burned in a 29-kW (100,000 Btu/hr) down-fired combustor under similar conditions. Flue gases were sampled for 10 metals: antimony, arsenic, beryllium, cadmium, chromium, lead, manganese, mercury, nickel, and selenium. No general correlation was found between coal sulfur content and metal emissions. The tests showed correlations between as-fed metal content in the coal, and uncontrolled measured emissions of the metal changed as the coals changed. The factor determining the degree of correlation appears to be metal vapor pressure. The study illustrates that predictions of metal emissions based only on the trace metal content of the coal may not be accurate.