The paramagnetic contributions to the spin-lattice relaxation rates of biotin13C nuclei, induced by the presence in the water/DMSO solution of the TEMPOL nitroxide, have been analysed in the interaction with avidin. The paramagnetic relaxation data, obtained at different temperatures, indicate that the average solvent/spin-label exposure of biotin carbons is consistent with the conformational features previously observed for the complex in the crystal. The analysis of the paramagnetic perturbation profiles, derived from13C spin lattice relaxation measurements, seems to be highly informative of the sterical aspects of interaction processes of large biopolymers with their ligands.