The evolution of CO2 concentrations in selected soils of the Moravian Karst (Czech Republic) was studied during a 1-year period from August 2008 to July 2009. CO2 concentrations directly measured in air of the soils of coniferous and deciduous forests reached up to 0.5 vol%. Substantially, higher CO2 concentrations, over 1 vol%, were found in thicker sinkhole soils under grassy vegetation. CO2 concentrations showed strong seasonality with maxima in summer and minima in winter at all sites. On the basis of temperature dependence, ln cCO2 = b0-b1/T(where cCO2 is CO2 concentration in mol/L, T is temperatures in Kelvin, and b1, b2 are constants); all CO2 concentrations were normalized to 10°C. These concentrations did not correlate with rainfall or soil profile depth. The remaining maxima in the time series of CO 2 concentrations (a sharp peak especially in July) might be the result of increased plant respiration during enhanced photosynthesis activity during the early-summer stage of the green period.