In this study, 3-D kinematic as well as 2-D videorecordings were made of the reaching behavior of infants aged about 6 months who were not Yet able to sit, Detailed analyses of these recordings were directed toward specifying the effects of providing additional postural support to the lower body, on the spatial and temporal features of such behavior. To detect these effects, reaching and associated head movements in this modified condition were compared to those made while the infants sat in an age-appropriate and commercially available chair lacking the supplementation of support for the pelvic region and upper legs, Findings consistent with predictions included better head stabilization and smoother reaching movements when the infants were in the modified chair In addition, these two achievements were negatively related to reaching experience. These, and other findings, underscore the infrequently investigated supposition that changes in postural control induce improvements in the control of reaching movements during infancy. Recommendations are made about how the procedure adopted in the present study could be used in subsequent research to give further insights into the codevelopment of posture and action, (C) 2002 Periodicals, Inc.