Extrapolating from extensive field measurements on foliar emissions in the U.S. we arrive at approximate global inputs of isoprene and terpenes of 3.5¿1014 and 4.8¿1014 g(C)/yr respectively. The oxidation of these hydrocarbons could contribute in an important way to the atmospheric sources of CO (4.2-13.3¿1014 g/yr) and H2 (10-35¿1012 g/yr), and to organic species soluble in rainwater.