1.1. The phospholipoprotein nature of DDT-dehydrochlorinase (DDTase) purified from a DDT-resistant strain of houseflies has been made evident by isolation of the phospholipids by extraction of the enzyme with organic solvents and by gel filtration on Sephadex LH-20.2.2. Phosphorus analysis gave about 40 μmoles P per mole of enzyme. Eighteen per cent of it was directly extractable using organic solvents; the remaining 82 % was extracted only after acid digestion of the protein, suggesting firmly bound phospholipid-protein residues.3.3. Phosphatidylcholine, phosphatidylserine and their lysoderivatives have been found in both DDTase extracted fractions.4.4. Fatty acids with carbon from C-12 to C-20 were identified by GLC. About twothirds corresponded to saturated fatty acids, with palmitic and stearic acids predominating. Among the unsaturated fatty acids, oleic and palmitoleic acids were found to occur at high levels.