The concentration of atmospheric CO 2 was measured continuously in the suburbs of Sendai, Japan for the period December 1978-June 1981. The diurnal CO 2 variation was greatest in July and August and was barely observable during the cold months from November to April. The seasonal CO 2 variation was highly irregular and a decrease of CO 2 concentration with height was found throughout the year, presumably reflecting a substantial influence of local soil respiration. Daily minimum values of CO 2 concentration, however, showed a fairly regular seasonal trend and an average rate of CO 2 increase of 1.6 ppmv yr -1 . which are very close to the results of our aircraft measurements in the lower troposphere for the same period. DOI: 10.1111/j.1600-0889.1985.tb00042.x