A method is suggested for testing the biodegradability of insecticides using bacteria from a sewage lagoon. The proposal is based on results which showed that the biodegradable organophosphates Malathion, Parathion, and Diazinon were metabolized quickly by resting cell suspensions of lagoon bacteria while the persistent chlorinated hydrocarbons Heptachlor, Dieldrin, and DDT were metabolized poorly or not at all. Data also showed that oxygen was not an important regulator of catabolism for any of these insecticides. Heptachlor epoxide and DDD were the only metabolites identified. The advantages of the method are discussed.