[en] The relaxation behavior of the He--HD system is studied by applying an exponential distorted wave procedure to calculate the cross sections and the rate constants for vibrational--rotational energy transfer in the vibrational manifolds n, 0< or =n< or =5. The rotational states are shown to play an important role in vibrational relaxation by providing many pathways for vibrational--rotational--translational energy exchange. By comparison with breathing sphere calculations it is demonstrated that the near exponential growth in the n→n-1 rates from vibrotor calculations can be attributed not only to the vibrational anharmonicity but also to the decreasing rotational energy spacings as n increases