An inventory describing the fluxes of the volatile organic compound (VOC), isoprene, and the class of VOCs, the monoterpenes, from the biosphere to the atmosphere has been constructed for Great Britain (GB). The controlling parameters were emission potentials from individual plant species, plant species distribution, biomass distribution, temperature, and light intensity. Species distribution and cover data from a national survey of vegetation in 1990 were used. A database of monthly biomass factors was compiled and a qualitative database of VOC emission potentials from vegetation species was updated to a quantitative form. This was used in conjunction with a taxonomic methodology to assign isoprene and monoterpene emission potentials to each plant species extant in GB. Hourly meteorological data for 1998 were calculated using a three-dimensional nonhydrostatic meteorological mesoscale model (MM5) and these were used to predict the isoprene and monoterpene fluxes in GB in 1998 on a spatial scale of 12 ¿ 12 km and with an hourly temporal resolution. Estimates of annual biogenic isoprene and monoterpene fluxes were 8 and 83 kt, respectively, for the model year. Picea sitchensis (Sitka spruce) is the dominant emitting species in GB, emitting approximately 40% of the annual isoprene and monoterpene fluxes. The dominant emitting regions in GB are coniferous forests in Scotland (isoprene and monoterpenes) and a Populus spp. (poplar) rich area in eastern England (isoprene). Overall uncertainty in the estimates is a maximum of a factor of 4. A sensitivity analysis of the model was used to study the impact of changes in vegetation cover and climate on VOC emission.