1,1-Dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) and 1,1-dichloro-2, 2-bis(p-chlorophenyl)ethylene (DDE) levels were measured by capillary gas chromatography with electron capture detection in liver and blood serum of male F344/NCr rats exposed for 2 weeks to DDD at dietary concentrations ranging from 8.51 ppm to 2,000 ppm. DDD burdens in serum ranged from <0.006 microM (limit of detection) in control rats to 1.1 microM in the rats fed DDD at 2,000 ppm. The corresponding liver burdens in these animals ranged from <0.006 micromol/kg liver (controls) to 11 micromol/kg liver in rats fed DDD at 2,000 ppm. Levels of DDE in serum or liver were undetectable (<0. 006 microM in serum; <0.006 micromol/kg liver) in rats fed control diet or diet containing 8.51 or 25.5 ppm DDD. The liver and serum burdens of DDE increased with dietary DDD concentration, reaching a maximum of 0.53 microM in serum and 4.7 micromol/kg liver in rats fed 2,000 ppm DDD. As a percentage of total DDD equivalents detected in liver or serum, the DDE burdens increased to a maximum of 36% and 31% in the serum and liver, respectively, of rats fed 689 ppm DDD. The possibility that the DDE might have been generated artifactually in the diet prior to administration to the rats was ruled out by analysis with capillary gas chromatography of the diet containing 2, 000 ppm DDD. The identification of DDE as a metabolite in liver extracts of rats fed 2,000 ppm DDD was confirmed with GC-MS. The results confirmed the presence of DDE as a metabolite of DDD.