Several freshwater aquatic species were exposed to cadmium in site and laboratory water to evaluate an 'organism testing' protocol proposed by the U.S. Environmental Protection Agency for deriving site-specific, water quality criteria. The procedures of reclaculation, indicator species, and resident species were used in this protocol to modify the national maximum and 30-day average cadmium criteria. The site-specific, maximum concentration derived from the recalculation procedure was slightly lower than the national criterion value. The maximum concentration derived from the indicator species procedures was 7.0 micrograms/l and was calculated by using a water effect ratio from tests conducted in both site and laboratory water. Acute tests with several species demonstrated that cadmium was less toxic in site water than in laboratory water. Acute tests conducted monthly in site water showed that cadmium toxicity varied by more than a factor of three over the year.