1.1 ,This guide describes procedures for obtaining data concerning the adverse effects of a test material (not food) added to marine and estuarine waters on certain species of marine and estuarine mysids during 96 h of continuous exposure. Juvenile mysids used in these tests are taken from cultures shortly after release from the brood and exposed to varying concentrations of a toxicant in static or flow-through conditions. These procedures will be useful for conducting toxicity tests with other species of mysids, although modifications might be necessary.