Dimethylsulphide (DMS) in surface seawater and vertical hydrographic profiles were deter-mined in the western, subtropical, and tropical Pacific Ocean during the cruises of the Seisui-maru, Mie University (Cruises 86-R-9, 87-R-8, 88-R-5) and the Hakuho-maru, Ocean Research Institute, University of Tokyo (Cruise KH-88-1). The vertical distribution of DMS in the euphotic zone follows that of primary production, with a maximum at or near the ocean surface and a decrease with depth. Below the level of 1% light penetration, DMS levels decline gradually. The mean DMS concentrations in the surface water of the sea off Japan and the tropical and subtropical Pacific Ocean were 611 and 265ng DMS/l, respectively. Since DMS is the major volatile sulphur compound in the ocean, it is suggested that estimated DMS transfer across the sea-air interface contributes significantly to the atmospheric sulphur budget.