Salinity preferences of adult and young-of-the-year largemouth bassMicropterus salmoidesfrom a freshwater lake and a brackish marsh in south-central Louisiana were tested at 22°C in salinity-gradient chambers (0, 3, 6, 9, and 12‰ salinity) under a photoperiod of 12 h light 12 h dark. Young largemouth bass from both collection sites preferred 0‰ salinity. Although adult marsh and freshwater largemouth bass preferred 3‰ salinity, differences in salinity selection were noted: mean number of observations at 0‰ salinity was significantly greater for freshwater fish, whereas mean number of observations at 3‰ salinity was significantly greater for marsh fish. Salinity preferences were not affected by prior acclimation of fish to salinities of 0 or 5‰. Salinities of less than 5‰ did not influence short-term (daily) movements of marsh fish implanted with ultrasonic transmitters. Although no tagged largemouth bass could be located in the marsh after salinities exceeded 5‰, marsh largemouth bass smaller than tagged individuals were still present. Salinity is only one component of the biologically and physicochemically complex marsh environment, but it does appear to be an important factor that influences seasonal abundance and movement patterns of marsh largemouth bass.