To quantify the postural adjustments over time, twelve normal subjects were investigated with posturography during vibration either toward the calf or the paraspinal neck muscles; with eyes open vs. eyes closed. The stimulus response adjustments over time were found to be almost identical for all test conditions, though the responses were smaller during eyes open conditions. To determine the response adjustments and thus the dynamics of postural control, a system identification methodology incorporating both step response and dynamic feedback components was developed. This methodology can be used to quantify both short-term stimulus response and postural adaptive adjustments when evaluating postural control performance. Copyright 1998 Elsevier Science B.V.