The relationship between affective responsiveness, synchrony of mother/infant interaction, and developmental status was examined in 32 normal infants (eight infants each at the ages of 4, 8, 12, and 16 weeks). Data were collected in infants' homes and included (1) naturalistic mother/infant play; (2) presentation of auditory, tactile, visual, and social stimuli patterned after Sroufe and Wunsch (1972); and (3) Uzgiris-Hunt and Bayley assessments. Results revealed emerging relations between affect, cognition, and synchrony. Infants of high versus low synchrony differed in their preferences for and variability of responsiveness to varying types of stimuli; synchrony emerged as a possible organizer and facilitator of development. These data suggest that the relation between early affect and cognition may be most meaningfully examined within the context of mother/infant interaction and that further investigation is mandatory, with implications for early infant assessment. (Author)