A quantitative method for the unified extraction of organochlorine and organophosphate insecticides contained in waters at microgram per litre concentrations is described. Recoveries of parathion-methyl, diazinon, malathion, azinphos-methyl, γ-BHC, heptachlor epoxide, aldrin, dieldrin, endrin, pp′-TDE, pp′-DDT and methoxychlor added to seven lake waters and distilled water ranged from 93·9 to 102·4 per cent. Recoveries of heptachlor ranged from 81·0 to 88·0 per cent., apparently because of degradation of the insecticide in aqueous systems.