Verbal/vocal interactions of three Japanese mother–child dyads were examined when the children were 1;0, 1;2 to 1;3, 1;6 to 1;7, and 1;8 to 1;9 to determine whether mothers provide information which may facilitate the elaboration of child lexical forms during the transition from the prelinguistic to the linguistic period. Mothers were likely to reproduce only the child's word-like utterances, both well- and ill-formed. This provided an opportunity for the child's ill-formed word-like utterance to be contrasted with an immediate maternal response. This finding, along with results showing within-child variability of lexical forms, suggested that maternal contrastive replies 1) signal errors to the child (cf. Saxton, 1997), and 2) may promote the child's selection and stabilization of production alternatives which are more accurate. Maternal reproductive responding presumably originated in their tendency to seek content-oriented communication, as was reflected in mother's growing inclination to continue verbal interactions following the child's non-word-like vocalizations.