Air samples in ice cores from Site J, Greenland and Mizuho, Antarctica were analyzed to reconstruct the past concentrations of atmospheric CH4 at northern and southern high latitudes. The results showed that the CH4 concentrations were fairly constant in the pre-industrial/pre-agricultural era covered by this study, average values being 756¿10 and 701¿10 ppbv for the Site J and Mizuho cores, respectively, and then increased significantly with time. The pre-industrial/pre-agricultural levels of the CH4 concentration obtained from the Site J core were higher by 55¿20 ppbv than those from the Mizuho core, suggesting that natural CH4 sources had been stronger in the northern hemisphere than in the southern hemisphere. ¿ American Geophysical Union 1993