The concentration of pp'DDT, pp'DDE, pp'DDD, and op'DDT in the fat and blood of sheep was dctermined for 24 weeks after a smgle administration of technical DDT (50 mg/kg b.w.); op'DDT and pp'DDD were eliminated more rapidly than pp'DDT. The most marked feature was the persistence of pp'DDE. which increased and then remained at a plateau level throughout the experiment.