The method of mode superposition has been much applied in regional-distance seismology to synthesize the complex seismic phases recorded in that distance range. As it is conventionally applied, however, this method can lead to significant errors in the calculation of regional seismic phases. The errors follow from the manner in which perturbation theory is employed to accommodate anelastic losses, and specifically from the use of the unperturbed (elastic) eigenfunctions to compute the mode residues for the anelastic problem. Resulting inaccuracies are most likely to be important when the intrinsic quality factors are strongly depth dependent. For a fairly realstic velocity and Q model of the Basin and Range, for example, mode superposition synthetics for an explosion source underestimated Pn and Pg amplitudes by about a factor of 2. ¿ American Geophysical Union 1989