Research has demonstrated the usefulness of the Microtox™bioassay in assessing the acute toxicity of organic compounds. Recently, the use of the Microtox™bioassay has been extended to applications in hazardous waste management. The rapidity of the test, low sample requirements, and low cost provide several advantages over chemical analysis, especially for complex waste mixtures. Microtox™bioassay results correlate closely with results from rainbow trout bioassays, and are more sensitive to inhibitory chemicals than activated sludge organisms. An experimental approach using batch reactors and soil columns was implemented in the laboratory to evaluate the detoxification and mobility of a toxic complex hazardous waste in soil. The objective of the study reported here was to quantify the extent and rate of detoxification of a complex hazardous waste as affected by soil type and waste application rate. The extent and rate of detoxification was directly related to waste loading rate for both soil types investigated, in both batch reactors and soil column reactors. Analysis of the toxicity of aqueous soil extracts at incremental depths through soil columns and of soil columnn leachate indicated a low leaching potential for the complex petroleum refinery waste.