Methods for evaluating adverse effects of toxic substances rely on having test organisms of known size and age (usually juvenile) available for testing. Culturing test organisms often consumes much of the research effort leaving less time available for field evaluations of contamination. Additionally, taking healthy organisms to the field for onsite testing is often problematic. The goal of the research described below was to evaluate one microscale test, a growth test using ciliate protozoa, 1 for use in a battery of tests approach to contaminant and site evaluation. Microscale tests using ciliates satisfy two needs: the selected test organism reduces the need for long-term culturing and is representative of small, rapidly responding bacterivorous species in soils and freshwaters.