An individual assignment of certain peaks in the proton and 13C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off‐resonance decoupled 13C spectra of bilirubin dimethyl ester. The signals due to the endo and exo vinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin‐lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation time.