The first optically active taurine conjugate of a bilirubin was prepared by reaction of taurine sodium salt with the mixed anhydride formed from reaction of (betaS,beta'S)-dimethylmesobilirubin-XIIIalpha with isobutyl chloroformate. Analysis of the circular dichroism spectra of the conjugate in water and chloroform indicate a conformational preference for the (M)-helical ridge-tile conformation, thus providing the first spectroscopic evidence on the conformation of ditaurobilirubins.