We measured dimethylsulfide (DMS) concentrations over a grid of 79 stations covering the central part of the Gulf of Saint Lawrence and during a 24-hour sampling period at a fixed station, in August 1993. Surface water DMS concentrations ranged from <0.9 to 9 nM over the sampling grid. DMS sea-to-air fluxes ranged from <0.1 to 23 μmol m-2d-1, with a mean of 4.7 μmol m-2 d-1 for August. Atmospheric DMS levels measured during the cruise ranged from less than 0.5 nmol m-3 (12 parts per trillion by volume, or pptv) to 25 nmol m-3 (625 pptv) with a mean value of 11.9 nmol m-3 (291 pptv). Results from the 24-hour sampling at the fixed station show that ventilation may represent the most important sink for surface DMS when wind speeds exceed approximately 8 m s-1. The relative magnitude of the biogenic and anthropogenic S components was estimated by comparing sulfur emissions from the gulf to the sulfur emissions from surrounding continental regions and to a sulfur budget calculated by using a Lagrangian box model. The first approach suggests that DMS emissions from the gulf represented at least 4% of total (biogenic plus anthropogenic) sulfur emissions from the Atlantic Provinces in August 1993. A Lagrangian forward motion trajectory shows that these biogenic emissions would affect all the Maritime Provinces and a portion of eastern Quebec. The second approach suggests that the contribution of the gulf to the total sulfur flux may reach 13% when compared with the anthropogenic inflow of sulfur from the Atlantic Provinces impacting the Maritimes. When the transboundary inflow of sulfur from the United States is also taken into account, the contribution of the gulf becomes 8%. Thus DMS emissions from coastal waters may represent a significant source of sulfur to the atmosphere. ¿ 1997 American Geophysical Union