The osmoregulatory capabilities of the grass shrimps Palaemonetes kadiakensis Rathbun, Palaemonetes pugio Holthuis and Palaemonetes vulgaris (Say) were compared with steady-state and nonsteady-state experiments conducted to measure hemolymph chloride concentration, hemolymph osmolality, standard oxygen consumption and tissue free amino acid concentration. In addition, starch gel electrophoresis was used to compare genetic variability among Palaemonetes populations.