A new experimental measuring system for the total gaseous mercury saturation in the sea surface water has been developed. The technique applied to the system is based on equilibrating water-air mercury partial pressures at the air-sea interface. First data using this system were collected in the Baltic Sea on 13-22 January 2000. Measurements were completed from the research vessel 'Alexander von Humboldt' on the way from the Gotland Sea to the Mecklenburg Bight. In general the results showed domination of supersaturated winter sea surface waters with respect to gaseous mercury. Two areas with distinctly elevated mercury saturation were found: one in the east-west shipping route, south of Bornholm, where the equilibrated gaseous Hg content of water was approximately 9.2-fold higher, and another over the ammunition disposal region south-east of Hoburgs Bank, where the Hg content of water was approximately 3.8-fold higher than that in air. In general, the data indicate that the south-western Baltic Sea, and in particular both maritime areas identified with elevated mercury saturation, can emit gaseous mercury from surface waters into the atmosphere and contribute to long-range atmospheric transport.