The article describes the results of field studies carried out in the period from April 2013 to May 2014. The study concerned the assessment of the magnitude of CO2 emissions from marsh soils in the area of Czerwone Bagno (Red Swamp), which is a part of the largest complex of marsh in Poland. The authors used the closed chamber method to measure seasonal variability of net ecosystem CO2 emission and drew attention to the impact of environmental factors (air temperature, air pressure and soil moisture) on it. The highest values of average daily CO2 emission (over 630 mg(CO2)×m–2×h–1) were recorded in late spring and summer. Lowest values were obtained in late autumn and winter (in the range of 178-212 mg(CO2)×m–2×h–1). The need for monitoring of wetlands in temperate latitudes is stressed due to the progressive process of wetlands drying which enables the release of large quantities of greenhouse gases – CO2, CH4 – into the atmosphere.