The theoretical importance of the linguistic data available to the child in his natural environment has been increasingly emphasized in recent work on child language acquisition. This study sought to describe a portion of such data as contained in maternal verbal behavior and to analyze its influence on the child's usage of speech. The subjects were five 21-month-old children and their mothers. The mother-child verbal interchange was recorded during free-play situations carried out both at the subject's home and in a playroom. The interactive patterns of mother-child utterances were analyzed with regard to the kind and frequency of verbalizations, and the temporal intervals between them. Results showed that the temporal pattern of mother-child interchanges was characterized by significantly shorter pauses (<2 s) for mothers than for children. A variation in this pattern, consisting of pauses longer than 4 s, was associated with certain kinds of ongoing mother-child verbal behaviors. Thus mothers showed selectiveness, in varying degrees, in responding to the child's utterances, and their verbal responses had differential effects on the child's subsequent verbal performance. These effects were described as “initiating”, “maintaining”, or “ending” verbal chains, or else as “non-reacted” utternances. Moreover, the amount of verbalization by the children was positively correlated with the proportion of the mother's output that consisted of immediate responses to the child, and not with the total verbal output.