Phthalates, e.g. dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), benzylbutyl phthalate (BBP), and di-(2-ethylhexyl) phthalate (DEHP) were measured in the atmosphere and sea water of the North Sea (German Bight). The air and water samples were collected during an expedition cruise with German research ship 'Gauss' in the North Sea from 29th February to 10th March 2004. The concentrations of phthalates in the atmosphere ranged from below the method detection limit to 3.4 ng m-3. DBP, BBP, and DEHP were determined in the water phase with concentrations ranging from below the method detection limit to 6.6 ng L-1. Air-sea vapour exchange of DBP, BBP, and DEHP was estimated using the two-film resistance model based upon relative air-water concentrations. The average of air-sea exchange fluxes was -338 ng m-2 day-1 for DBP and -13 ng m-2 day-1 for BBP, which indicates a net deposition is taking place. The air-sea exchange fluxes of DEHP were ranging from -95 to +686 ng m-2 day-1. The average value of +53 ng m-2 day-1 for DEHP suggested a net volatilization from the North Sea. Moreover, the particle-associated fractions were calculated as 2%, 46%, 75% and 78% for DEP, DBP, BBP and DEHP, respectively. These results indicate that the air-sea vapour exchanges is an important process that intervenes in the mass balance of phthalates in the North Sea. © 2005 Elsevier Ltd. All rights reserved.