Trace quantities of the polynuclear hydrocarbons have been identified in flue gases resulting from combustion or carbonaceous fuels. Some of these hydrocarbons, particularly benzo(a)pyrene, possess known carcinogenic properties and are of some concern in the overall assessment of the effects of atmospheric pollution. An investigation was carried out under a two-year grant received from the U. S. Public Health Service to determine the occurrence of polynuclear hydrocarbons in the flue gases from various coal-fired steam-generating installations. The paper describes the preliminary work leading to the development of satisfactory sampling and analytical procedures and gives the results obtained from sampling various field installations.