We have been measuring concentration of atmospheric CO2 and its carbon isotope composition in the Kraków region for about two years. Samples are continuously collected at two-week intervals at ca 20m above ground level, close to the center of the industrialized urban area. Sampled atmospheric CO2 is sorbed in a molecular sieve and, after recovery by heating, is converted to benzene. 14C is measured in a liquid scintillation spectrometer, and δ13C of the CO2 is determined in a mass spectrometer. The annual record shows winter-summer variation of 14C, 13C, and CO2 concentration. A long-term trend for 1983 and 1984 indicates a slight decrease of 14C activity (1 22.0 in January 1983; − 1.2% per year), a permanent decrease of δ13CPDB (−9.3‰ in January 1983; −0.3% per year) and an increase of CO2 concentration (344 ppm in January 1983; 1.4ppm per year).