The toxicity, adsorption, and leaching of 4 herbicides in different soils were determined by a method based on a sensitive root bio-assay which appeared suitable for herbicides affecting root growth. The rate of leaching of the herbicides was determined by measuring the herbicidal effect of the leachate obtained from three heights of soil columns. The same bio-assay was utilized for testing the extent of inactivation of herbicides due to adsorption by soil. In this case, mixtures of various rates of soil with silica sand were used as cultures for the bio-assay.