A biogenic hydrocarbon emission inventory system was developed for the northeastern United States with design options for extension to other areas. Emissions from trees, leaf litter, crops, grass, and water are estimated for cells of 1/6 degrees latitude by 1/4 degrees longitude (about 20 km x 20 km). Hourly emissions were calculated for the period, July 23-26, 1980, and compared with anthropogenic hydrocarbon emissions from the NAPAP inventory. Natural hydrocarbons appear to represent 60% of the regional VOC emissions. Output from the biogenic inventory is structured to provide isoprene and other VOC input compatible with the Carbon Bond IV photochemical kinetic reaction system employed in the Regional Oxidant Model.