Four isocyanates are listed for regulation in the Clean Air Act Amendments of 1990: hexamethylene-1,6 diisocyanate, methylene diphenyl diisocyanate, and 2,4-toluene diisocyanate, each of which is used in the production of polymers, and methyl isocyanate which is an intermediate in the manufacture of insecticides. To support projected regulations, a study is under way to produce a source sampling and analysis method for the four pollutants cited above. In the procedure under development, the isocyanates are collected in a modified Method 5 sampling train and stabilized with a derivatizing reagent, 1-(2-pyridyl)piperazine in toluene. Derivatized samples are then returned to the laboratory and analyzed by High Performance Liquid Chromatography with UV detection (HPLC-UV). An isocyanate generator was developed in the laboratory to provide isocyanate atmospheres for optimizaton of sampling parameters and chromatographic conditions. The accuracy and precision of the method is determined in the field using train spiking and multiprobe sampling techniques, following the procedures outlined in EPA Method 301.