Since approximately 90% of hazardous wastes reach soil and water for permanent disposal, it is logical that microflora (bacteria) contained in these environments be used to establish initial toxicity levels. Bacteria can be suitable bioassay tools because they are inexpensive to cultivate, grow rapidly and have physiological and enzymatic processes also found in higher organisms. A screening bioassay needs to be accurate, inexpensive, rapid, and sensitive. The bioassay described in this study meets these criteria and utilizes bacteria as the toxicity predictor. The basis of the test involves measuring the kinetics of dissolved oxygen depletion by a mixed microbial population following exposure to a pollutant and allows results to be obtained in as little as 40 min.