Although marine organisms are adapted to naturally high concentrations of total dissolved solids (salinity) in their environment, abnormally high or low concentrations of ions can be toxic. Toxicity can result from aberrant levels of a single ion or from shifts in the entire spectrum of salts that comprise saltwater. To determine how marine organisms will respond to drastic swings in solution salinity and to provide a predictive tool to assess toxicity attributable to salinity, three common marine test organisms were exposed to balanced solutions ranging in salinity from near zero to more than 80โฐ. The organisms tested were mysid shrimp (Mysidopsis bahia), sheepshead minnow (Cyprinodon variegatus), and inland silverside minnow (Menidia beryllina). Logistic regression was used to relate salinity to survival for each of the three test species. Survival of all three species was reduced at low and high salinities, although impacts to mysid shrimp at salinities of 4โฐ or less were more pronounced than to either fish species. In high-salinity studies, mysid shrimp and inland silverside minnows had 48-h LC50s of approx. 45โฐ; a 48-h LC50 of nearly 70โฐ was calculated for the sheepshead minnow. Mysid shrimp and sheepshead minnows were relatively consistent in their response to saline solutions, whereas silverside minnows were more variable in their response.