Determination of toxic organic compounds in ambient air is a complex task, primarily because of the wide variety of compounds of interest and the lack of standardized sampling and analysis procedures. The methods compendium has been prepared to provide current, written, peer-reviewed analytical procedures in a standardized format for analysis of toxic organic pollutants of primary importance in ambient air. A core set of five methods covering some 29 air toxic compounds was published in the original Compendium (EPA 600/4-84-041, 1984). Four additional methods were added to the Compendium in the first Supplement (EPA 600/4-87-006, 1986). The Second Supplement adds five more methods to the Compendium, bringing the total number of methods in the Compendium to 14, covering a wide variety of toxic organic air pollutants. The five new procedures are applicable to pesticides (T010), formaldehyde (T011), non-methane organic compounds (T013), benzo(a)pyrene (T013), and various toxic VOCs (T014). As further advancements are made, the current methods in the Compendium may be modified or updated, or additional methods may be added as appropriate.