ABSTRACT: The main goal of this study was to assess the effects of algal diets and water salinity on the bodily content of dimethylsulfoniopropionate (DMSP) in estuarine copepods. In laboratory experiments, Temora longicornis contained moreDMSP when fed DMSP-rich Tetraselmis impellucida (prasinophyte) than when fed DMSP-poor Dunaliella tertiolecta (chlorophyte). The DMSP content of T. longicornis after gut clearance was curvilinearly related to theingestion rate. These observations suggest that the copepods incorporated the dietary source of DMSP into their body tissue. On the same diet, T. longicornis contained more DMSP at higher salinity, indicating an osmoregulatory function ofDMSP. However, DMSP appears to be a minor osmolyte compared with free amino acids. The DMSP content of T. longicornis decreased faster in response to a decrease in salinity than it increased with an increase in salinity, implicating separatemechanisms for accumulation and removal of DMSP in the copepod. We also measured the bodily content of DMSP from field-collected animals. Five species of calanoid copepods from Long Island Sound contained DMSP, not associated with gut content, whichvaried interspecifically from 0.02 to 1.03 nmol ind.^-1. Carbon-specific DMSP content of the copepods was comparable to that reported for some diatoms, chlorophytes and cryptophytes. We argue that copepod biomass may, at times, represents asubstantial source of particulate DMSP in the water column.