DEMETER, a new process based model of the terrestrial biosphere, is used to simulate global patterns of net primary productivity (NPP). For the modern climate, NPP and vegetation biomass are simulated to be 62.1 Gt C yr-1 and 800.6 Gt C, respectively. Simulated NPP is found to be highly correlated to field observations (r=0.9343) and the results of the empirically based Miami model (r=0.9587). ¿ American Geophysical Union 1994