The chlorinated pesticide, endosulfan, could be degraded by Phanerochaete chrysosporium under non-ligninolytic conditions, and this did not require direct contact with mycelium. The major metabolites formed were endosulfan sulfate and endosulfan diol. The rate of degradation depended on the initial concentration. With 2.5 mg endosulfan l(-1), degradation was at 0.23 mg l(-1) day(-1). The degradation could be described using a nonlinear rate expression that was similar to the Michaelis-Menten equation.