ABSTRACTA flux chamber technique applied to volatile mercury species has been developed and evaluated. This technique can be used to measure the direction and magnitude of mercury transfer between the atmosphere and lake or soil surfaces. Measurements have been performed over four oligotrophic forest lakes in southwestern Sweden during 1988 and 1989. Net emission fluxes of mercury were measured from the lakes. The measured daytime fluxes during the warmer season (water temperatures 13–23 °C) were within the range 3–20 ng h−1 m−2 (average 7.9 ng h−1 m−2). The average night-time fluxes measured during the same season were 2 to 3 times smaller. Two sets of measurements, performed during the winter when water temperatures were ≤ 2 °C, gave flux values close to zero. Flux measurements were also performed over soil in a coniferous forest. Compared to the situation for the forest lakes, the fluxes of mercury over forest soil are much lower in magnitude, with values ranging from approximately − 2 to + 2 ng h−1 m−2 during different seasons. Emission was observed with an average of 0.3 ng h−1 m−2 when soil temperature was about 10 °C, while dry deposition was measured with an average of 0.9 ng h−1 m−2, when soil temperature was < 3 °C.