Chlorinated hydrocarbon insecticides persist in soil for many years because of their resistance to degreda-tion. Adsorption by soil colloids probably contributes also to their retention in soil. Microorganic accumulation of these compounds from distilled water was measured for Mucor ramannianus, Glomerella cingulata, Trichoderma viride, 3 streptomycetes, Bacillus subtilis, Serratia marcescens, and Agro bacterium tumefaciens. Results indicated that the ability to accumulate DDT and Dieldrin from culture solutions may be widespread among microorganisms. Accumulation occurred rapidly and over a wide range of pH and does not appear to involve metabolism.