Inflectional marking of person and number of subject in the verbs of Amuzgo (Eastern Oto-Manguean) involves various stem-internal morphophonological alternations. One such alternation type is in glottalization: stem vowels can alternate between laryngealized, post-glottalized, and plain versions in different paradigm cells. Based on an extensive database of verbal paradigms compiled by native speaker Fermín Tapia García, this paper establishes an inventory of glottalization classes for the San Pedro Amuzgos variety and proposes a hierarchy of morphophonological parameters which define all and only the five productive patterns. The approach follows feature-based analyses of inflectional class structure. I argue that it is possible to posit underlying forms plus a limited set of operations that derive the stem alternations, in a way that develops a theory of internal relationships among the glottalization classes. The proposed analysis makes predictions about natural-class behavior among glottalization classes, as well as impossible paradigm types, which appear to be borne out by the data.