Analyses provided in this paper test the possibility of morphological conditioning for vowel durations in Erzya. The duration of stressed first-syllable and unstressed second-syllable vowels in disyllabic ‘root’ and ‘inflectional form’ tokens was compared. Material consisted of one-word utterances produced in spontaneous speech by speakers of different dialects. The inter-idiolect vowel durations tended to equalize within the root. At the boundary of the root and a suffix vowels were shorter than in the stressed first syllable. The manifestations of the tendency varied across four idiolect groups representing the main language varieties. The results suggest that there is a causal relationship between unstressed vowel reduction and the domain of morphology. Dialects revealing variability in the manifestation of the general tendency towards vowel duration asymmetry in the root and inflectional forms also display differences in the mobility of stress, as suggested in previous research.