Research has demonstrated the occurrence of two structurally distinct modes of vocalization in the infant/mother pair--coaction and alternation--that change developmentally over the first year of the infant's life. The present study investigated the vocalization latencies of three infant/mother pairs at three stages of infant development: at 10 days of age, just prior to the predominance of alternation, and during the emergence of alternation predominance. Data collection consisted of videotaping in families' homes or in a university laboratory. Coaction was operationalized as the occurrence of overlapping infant/mother vocalizations; alternation was operationalized as infant vocalization(s) occurring between the offset of the mother's initial vocalization and the onset of her next. At all three time periods, mothers exhibited shorter vocalization latencies than their infants, and some infant/mother dyads responded faster to each other than did others. Although mothers' vocalization latencies were only slightly correlated at the three time periods, infants' vocalization latencies were moderately correlated just prior to and during the predominance of alternation. These findings suggest that mothers develop generalized temporal expectancies in relation to their infants' development of stable vocalization latencies and that these expectancies may in turn facilitate the development of alternation predominance in the infant/mother pair. (Author/RH)