1. Freezing point determinations were made on time blood of Crangon septemspinosa exposed to five salinities (15, 25, 30, 35, 45‰), at two temperatures (5, 15° C).2. Sand shrimp, transferred acutely from 30‰ to either 15‰ or 45‰, experienced changes in hemolymph osmoconcentration which were related to the osmotic strength of the receiving medium. A time period of about 4 days was required for the shrimp to reach a new steady state at 5° C.3. Crangon septemspinosa was observed to regulate its internal osmoconcentration to the extent that it was hyposmotic in normal seawater (30-35‰) and hyperosmotic in diluted seawater (15-25‰). In 45‰, adults were isosmotic but juveniles remained hyposmotic to the external medium.4. There was no apparent temperature influence on the regulatory pattern of juvenile shrimp. Adults, however, exhibited high blood concentrations at 15° C than at 5° C. They were, in effect, regulating more effectively in diluted seawater and less effectively in normal seawater at the warmer temp...