A novel UDP-glucuronosyltransferase that conjugates bilirubin IXα, bilirubin monoglucuronide and an arylalkanoic acid was purified to homogeneity from clofibrate treated Wistar rats. The enzyme displayed a subunit molecular mass of 54 kDa, a pI of 7.6 and was demonstrated to be N-glycosylated. Sequence analysis of peptides derived by endoproteinase Glu-C cleavage of the purified enzyme indicated that it was a new member of the recently identified UGT1 subfamily. Immunoblot analysis demonstrated that this enzyme was absent from Gunn rat liver. The molecular derivation of this enzyme and the lack of it in Gunn rats is discussed.