Examined was the association between affective and cognitive development in 14 Down's Syndrome infants (4- to 8-months-old). Mothers administered a series of 30 laughter items each month, and experimenters gave the Uzgiris-Hunt scales of cognitive development at 13 and 16 months, and the Bayley scales and Infant Behavior Record at 16 months. Available data indicated that Ss lagged well behind normal infants in onset of laughter and smiling although they followed the order of laughter items category by category (laughing first at auditory and tactile items and then at more cognitively complicated social and visual items). Results also demonstrated a clear relationship between cognitive and affective development, especially with regard to stages of object permanence and operational causality. (CL)