New isolation and detection methods were developed to measure dimethylsulfoxide (DMSO) and dimethylsulfone (DMSO2) in marine rain and marine air masses. Central equatorial Pacific rain contained 1 to 10 &mgr;g/l of each of these compounds. Uncontaminated air sampled off Miami contained 2 to 6 ng/m3 of each component. These concentrations suggest that DMSO and DMSO2 may be as significant as dimethylsulfide (DMS) in marine sulfur transport. In fact, DMSO was observed to undergo disproportionation in illuminataed seawater or distilled water to DMS and DMSO2. This latter observation implies a partially reversible loop in the sulfur transport cycle and complicates the calculation of the flux of sulfur into the marine boundary layer.