This longitudinal and naturalistic study aims to describe basic aspects of early imitative exchanges in dyadic infant-grandfather and infant-grandmother free interactions, from the second to the 10th month of age. Sixteen infants were video-recorded at home in the course of spontaneous dyadic interactions with maternal grandfathers and grandmothers; imitative interaction was characterised during off-line analysis of video-recordings. During interaction of infants with grandfathers and grandmothers, there was similarity in: (1) the frequency and the rate of imitation; (2) the structure of imitation, the number of turn-takings and the kind of co-actions; (3) the kind of imitated acts, totally and separately, the kind of imitated body movements, non-speech sounds, facial expressions and combinations; and (4) the temporal patterns of the components of turn-taking imitation. Differences were found for: (1) the direction of imitation, and (2) the linguistic nature of vocal imitations. Both grandfathers and grandmothers offer infants a sense of partner "stability" with similar and predictable actions and interactions--as evidenced by the similarities, as well as a "variety" of challenging communications--evidenced by the differences. It is assumed that grandfathers are as capable and sensitive as imitators and communicative partners as are grandmothers and parents. (Contains 4 tables.)