Mothers' verbal responses to their infants' spontaneous imitations of familiar and non-familiar words during naturally occurring interactions were examined in a longitudinal sample observed at 1 ; 1, 1 ; 5 and 1 ; 9. Maternal responses to both familiar and non-familiar imitations exhibited structural characteristics likely to be facilitative of early word learning, including shorter and single-word utterances and reproductions of imitated words in sentence-final position. Mothers also responded differentially to infants' non-familiar versus familiar imitations. Mothers produced more return imitations and more exact repetitions, providing an extra exemplar, following infants' imitations of non-familiar words. The familiar words infants imitated were more likely to receive the more complex expanded and reduced+expanded return imitations. Results suggest mothers' responses to infants' verbal imitations could serve as a mechanism for facilitating language acquisition.