In summer 1997 and winter 1998, paired boundary air and surface water samples were collected during cruises in the southern Baltic Sea. Simultaneously, deposition samples were taken at Gotland Island, located close to the air-water sampling area. Water samples taken shortly after the flooding of Oder and Wisla Rivers in summer 1997 were also included in the study. Concentrations and gas exchange fluxes of alpha- and gamma-HCH and chiral composition of alpha-HCH were determined. According to fugacity calculations, the HCHs were close to air-sea partitioning equilibrium. The net fluxes varied over time, particularly during summer. Importance of the air to sea removal routes "gross gas deposition" and "wet deposition" were about equal for gamma-HCH, while the scavenging via precipitation was less important for alpha-HCH. Enantiomer fractions were used to estimate the fraction of alpha-HCH in the boundary air layer that had volatilized from the water. During summer, the fraction was approximately 60%, and wintertime significantly less (0-35%). Variations in air mass origin were clearly reflected in net air-sea gas exchange and isomeric and enantiomeric "signatures" in boundary air. The composition of boundary air and precipitation was also variable depending on season.