Video-analysis was used to investigate the transition from coacting to alternating patterns of infant-mother vocalizations in this longitudinal study of one infant. In addition to investigating the transition and its developmental implications, the relationship between the temporal patterning of kinesic and vocal behaviors was studied. The study began when the infant was 3 and 1/2 months of age and ended when the child was 13 and 1/2 months old. A 3/4 inch color television camera was employed to tape a routine cycle of activity, usually on a bi-monthly basis. Each session taped was divided into feeding and play periods. Coaction was operationalized as the occurrence, within each session, 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 vocalization without overlap with her infant's vocalization(s). The infant's state of arousal was also assessed. A test-retest reliability check of an observer's and a graduate student's ratings of coaction and alternation indicated correlations of .79 and .99 respectively. Transition to alternation occurred when the infant was approximately between 4 and 4 and 1/2 months of age and progressed developmentally. Results are discussed in relationship to the temporal requirements of turn-taking and rhythmic aspects of adult conversation. (Author/RH)