This paper presents the results of study on unconfined groundwater table fluctuations induced by barometric pressure changes. Integrated Monitoring of the Natural Environment Programme (IMNE) research catchment located within the Kampinos National Park near Warsaw was selected as the study area. The network of 16 piezometers is located in the research catchment and the groundwater levels have been measured there in diurnal time-step since 1994. Atmospheric pressure data were collected via NCDC and Ogimet services from the nearest Institute of Meteorology and Water Management (IMWM) synoptic station Warsaw - Okęcie. Collected data series covered the period from 1994 to 2009. Events of the greatest daily changes in barometric pressure accompanied by groundwater level response (so-called mirror reaction) were selected in the first step. Barometric efficiency was estimated then on that basis. Also the differences in groundwater level response at the time of increase and decrease in atmospheric pressure and during high and low water levels were analyzed. It was found that the barometric efficiency in the piezometers varied from 4 to 16%, which was consistent with the results of other authors. Unfortunately, the divergent results, provided by different methods for estimation of barometric efficiency made the interpretation of data more difficult. Piezometers of water level from 50 to 100 cm represented clear response to barometric pressure changes. However, shallower and deeper water levels did not show an expected effect. Most likely those piezometers were controlled by other factors, such as precipitation, evaporation, infiltration or lateral flow. Using of more detailed (e.g. hourly) data series is highly recommended for further investigations.