EPA Method 101A applies to the determination of particulate and gaseous mercury emissions from sewage sludge incinerators and other sources. Concern has been expressed that ammonia or hydrogen chloride (HC1) when present in the emissions, interferes in the analytical processes and produces a high positive bias in the mercury results. Because HCl and ammonia are present in the effluents from municipal waste incinerators where chlorinated plastics are combusted, the present laboratory study was conducted to investigate these concerns. A standard EPA Method 101A sampling train was employed in the study. The source of Hg vapor consisted of two certified Hg permeation tubes. The mercury vapor was directed into a stream of filtered laboratory air and sampled at rates varying between 15 and 30 L/min. Approximately 1 m3 of gas was collected in each sample run. A side stream of ammonia vapor was added to the gas sampled in half of the runs to determine the effects of that substance. Mercury recoveries with and without added ammonia were 97.3 + or - 3.4 and 96.8 + or - 1.3%, respectively. Application of the Aspin-Welch test for the difference between two sample means showed that the difference was not statistically significant. The effect of added HCl was also studied. Mercury and HCl were added to samples of the acid permanganate reagent and subjected to the Method 101A analytical procedure. Mercury recoveries were 100.0 + or - 5.2, 101.3 + or - 8.5, and 98.0 + or - 5.4% for 0, 1, and 7 g of added HCl, respectively, indicating no effect of HCl on the analysis.