Two short-term bacterial toxicity tests that have received a great deal of attention during the last few years are the Microtox and Spirillum volutans assays. The former involves monitoring changes in the light output from luminescent bacteria (Photobacterium phosphoreum) in a temperature controlled photometer when exposed to various concentrations of toxic substances. In the S. volutans assay, motility patterns of this large aquatic bacterium are used as the test endpoints. As part of the authors' program in assembling and establishing a battery of short-term bacterial toxicity tests, they examined the use of Microtox and S. volutans for determining the toxicity of a wide variety of environmental samples. Samples examined included potable and surface waters, industrial effluents, soil/sludge extracts and landfill leachates. Some of the results are presented in this paper.