1. When 1,1-bis(p-chloro(14C)phenyl)-2,2,2,-trichloroethane (DDT) was fed to CF-1 mice and Syrian golden hamsters, conjugates of bis(p-chlorophenyl)-acetic acid (DDA) were the major urinary metabolites. As well as DDA-glycine, DDA-alanine and DDA-glucuronic acid previously identified, a new conjugate with serine is reported. 2. Small amounts of non-polar metabolites were detected in urine. Mouse urine contained DDE, whereas this was never detected in hamster urine. The relevance of this finding to the tumorigenicity of DDT in mice, compared with its inactivity in this respect in hamsters, is discussed.