Dimethylsulfoxide (DMSO) is an ubiquitous, albeit poorly understood, component of the marine sulfur cycle. Conventionally, the accepted formation pathways are the photochemical and microbial oxidation of dimethylsulfide (DMS). The principal loss mechanism is thought to be via microbial transformation, either consumption or reduction to DMS. The intel actions between DMSO and DMS are likely to be important in controlling sea surface concentrations of DMS, and thus DMSO could influence the role played by DMS in global climate regulation. This review examines current knowledge of the distribution of DMSO in aquatic environments and the possible link between DMSO, DMS and global climate control. Mechanisms for the formation and loss of DMSO are also considered in addition to some of the factors influencing these processes. The review also considers that DMSO may be biosynthesized by phytoplankton, representing a non-DMS source for DMSO, and that DMSO can undergo photochemical oxidation, a potential loss mechanism for DMSO in. the marine environment.