Gait initiation is a transient movement between upright posture and steady-state gait. Kinematic, kinetic and electromyographic data have been documented in healthy young subjects. However, there is little published data on the elderly and on Parkinson's disease (PD) subjects who are known to 'freeze' when initiating gait. It was the purpose of this project to measure gait initiation in young, healthy elderly and PD subjects. The results showed many differences between the young and elderly and the elderly and PD subjects. However, if all dependent variables were normalized to gait velocity there were no differences at the P<0.05 level. The results showed a progressive slowing from the young to the elderly to the PD subjects. There does not appear to be a relationship between the PD subject's steady-state velocity and their age, number of years diagnosed, number of hours off medication, or the rating on the Hoehn and Yahr scale. Copyright 1998 Elsevier Science B.V.