The potential of relaxation measurements for the detailed study of side-chain dynamics of peptides is explored. As a test case, the phenylalanine side chains with two rotational degrees of freedom in the cyclic decapeptide antamanide have been selected for the study. Various combinations of motional models, such as discrete jump and rotational diffusion models, have been considered for the two degrees of freedom. Although some ambiguity in the assignment of the different motional models remains, valuable information on the detailed side-chain dynamics can be obtained.