A novel method is presented for the measurement of relaxation properties of methyl group deuterons in proteins uniformly C-13 labeled and fractionally deuterated. The experiments select for (CH2D)-C-13 methyl groups and make use of the excellent resolution provided by constant time C-13-H-1 correlation spectroscopy to measure the H-2 relaxation rates, 1/T-1 and 1/T-1 rho, at all methyl positions in the protein. Since the relaxation of a deuteron is completely dominated by the quadrupolar interaction, interpretation of the relaxation data is more straightforward than is the case for relaxation data from other nuclei, where the relaxation rates often contain contributions from a number of interactions. The experiments are applied to study the sidechain dynamics of the C-terminal SH2 domain from phospholipase C-gamma 1.