Land treatment is categorized as an option to treat hazardous organic waste in soils. This treatment relies on detoxification, degradation, and immobilization of hazardous wastes constituents within the defined treatment zone to ensure the protection of surface water, groundwater and soil. The use of an appropriate battery of acute toxicity screening tests provides an acceptable method to estimate the initial application rates to be used in subsequent land treatment systems. This paper describes the Microtox acute toxicity test that has been developed and proposed by EPA - Environmental Protection Agency, to estimate the initial loading rates in a land treatment unit (EPA, 1986). The procedure involves conducting a sequence of Microtox tests on the water-soluble fraction of the soi], the waste, and selected waste-soil combinations. The results are used to establish a range of loading rates, which graphically are correlated with the EC50 or TU (toxic unit) to define the test loading rate which does not impact the biological activities of soil microorganisms.