We report the first detailed soil CO2 efflux survey carried out at Cerro Negro volcano, Nicaragua, Central America. Soil CO2 efflux values ranged from 0.5 to 35,000 g m-2 d-1. Spatial distribution of CO2 efflux shows that volcanic gas is mainly released from the summit crater and the fissures opened during the August 1999 eruption. The total CO2 output of Cerro Negro is conservatively estimated to be 2,800 t d-1, based on a study area of 0.58 Km2. Contour maps of soil CO2 efflux, ground temperature, and Δ13C(CO2) distributions support an important magmatic contribution for the total output of CO2 at Cerro Negro volcano. ¿ 2001 American Geophysical Union