1.1 ,This guide covers procedures for obtaining laboratory data concerning the adverse effects of a test material added to growth medium on growth of certain species of freshwater and saltwater microalgae during a static exposure. These procedures will probably be useful for conducting short-term toxicity tests with other species of algae, although modifications might be necessary. Although the test duration is comparable to an acute toxicity test with aquatic animals, an algal toxicity test of short duration (72, 96 or 120 h) allows for examination of effects upon multiple generations of an algal population and thus should not be viewed as an acute toxicity test.