Crude enzyme from a soil fungus, Aspergillus flavus, was isolated from a field soil following repeated applications of metolachlor [2-Chloro-N-(methoxy-1-methylethyl)-2'-ethyl-6'-methyl acetanilide]. Metolachlor hydrolysis by the crude enzyme extract was determined by enzyme assay. The tests were performed in phosphate buffer, pH 7.5, and the reaction was carried out at two herbicide concentrations (20 and 100 microg mL(-1)) and two crude extract volumes (0.2 and 0.5 mL of the homogenized crude extract mixture). The rate of metolachlor degradation was found faster in samples containing higher volume of crude extract, (T(1/2), 5.7 h) for both concentrations of the herbicide. The activities of enzymes responsible for dechlorination coupled with hydroxylation, N-dealkylation, and breaking of amide linkage were found responsible in the degradation.