In sampling gaseous hydrochloric acid in combustion source emissions by the standard method (collection of particles in a probe plug followed by absorption of gaseous HCl in an impinger solution), there is a potential for error due to interaction of HCl with the filtering medium and/or with particles on the filter. A laboratory study was conducted to examine the interaction of gaseous HCl with glass and quartz media and with particles from coal‐fired and incinerator boilers. Also, some source sampling results obtained by different methods at cement production plants, oil‐fired boilers, and a coal‐fired boiler were examined. On the basis of both studies, it is recommended that sampling for gaseous HCl in combustion source emissions employ a quartz filter medium, high‐velocity sample flow, minimum filter temperature, and minimum sample volume. This approach is expected to yield the most accurate HCl mass emission rates for source categories having significant chlorine in fuels or processes.