The purpose of the study was to investigate the relationship between mother-infant vocal patterns and emotional expression. Four mothers and their six month old infants were videotaped in the mothers‘ own homes during the infants 6–8 month of life. A coding scheme was devised to record the nature of the mother-infant dialogue. It was found that mothers and to a lesser extent infants adjusted and modified the timing of their utterances in relation to their partner's emotional state. The mothers content and form of vocalization also changed in relation to infants emotional state. There were no developmental changes across the 6–8 month period in the temporal patterning of the subject's vocalizations. Comment was made upon the important role emotional expression may play in regulating interaction during the first year of life.