A recently reported borohydride reduction method for the trace determination of aqueous dimethyl sulfoxide (DMSO) was adapted for use with a different sample preparation and analytical system, and the adaptation and optimization steps that we followed gave us further insight into the method. Increasing the proportion of reducing agent was critical. A number of compounds with potential for analytical interference were tested, but all proved negative. Water blanks were problematic, with substantial DMSO contamination observed in all but very recently purified water. Preliminary comparison with the highly specific and precise enzyme-linked method gave very good agreement. When DMSO analysis was done sequentially after analysis of dimethyl sulfide and alkali hydrolysis for dimethylsulfoniopropionate, we found that the DMSO concentration was not affected by increasing the length of the hydrolysis step. This allows storage and/or transport of hydrolyzed samples in gastight containers. The adapted method was applied to the novel determination of DMSO on glass fiber filters, and this revealed a significant pool of particulate DMSO in marine particles.