An NMR experiment is presented for the measurement of the time scale of methyl side-chain dynamics in proteins that are labeled with methyl groups of the (CHD2)-C-13 variety. The measurement is accomplished by selecting a magnetization mode that to excellent approximation relaxes in a single-exponential manner with a T-1-like rate. The combination of R-1((CHD2)-C-13) and R-2((CHD2)-C-13) H-2 relaxation rates facilitates the extraction of motional parameters from (CHD2)-C-13-labeled proteins exclusively. The utility of the methodology is demonstrated with applications to proteins with tumbling times ranging from 2 ns (protein L, 7.5 kDa, 45 degrees C) to 54 ns (malate synthase G, 82 kDa, 37 degrees C); dynamics parameters are shown to be in excellent agreement with those obtained in H-2 NMR studies of other methyl isotopomers. A consistency relationship is found to exist between R-1((CHD2)-C-13) and the relaxation rates of pure longitudinal and quadrupolar order modes in (CH2D)-C-13-labeled methyl groups, and experimental rates measured for a number of proteins are shown to be in excellent agreement with expectations based on theory. The present methodology extends the applicability of H-2 relaxation methods for the quantification of side-chain dynamics in high molecular weight proteins.