ABSTRACT: BACKGROUND: Gait-lines, or the co-ordinates of the progression of the point of application of the vertical ground reaction force, are a commonly reported parameter in most in-sole measuring systems. However, little is known about what is considered a "normal" or "abnormal" gait-line pattern or level of asymmetry. Furthermore, no reference databases on healthy young populations are available for this parameter. Thus the aim of this study is to provide such reference data in order to allow this tool to be better used in gait analysis. METHODS: Vertical ground reaction force data during several continuous gait cycles were collected using a Computer Dyno Graphy in-sole system(R) for 77 healthy young able-bodied subjects. A curve (termed gait-line) was obtained from the co-ordinates of the progression of the point of application of the force. An Asymmetry Coefficient Curve (AsC) was calculated between the mean gait-lines for the left and right foot for each subject. AsC limits of +/- 1.96 and 3 standard deviations (SD) from the mean were then calculated. Gait-line data from 5 individual subjects displaying pathological gait due to disorders relating to the discopathy of the lumbar spine (three with considerable plantarflexor weakness, two with considerable dorsiflexor weakness) were compared to the AsC results from the able-bodied group. RESULTS: The +/- 1.96 SD limit suggested that non-pathological gait falls within 12-16% asymmetry for gait-lines. Those exhibiting pathological gait fell outside both the +/- 1.96 and +/- 3SD limits at several points during stance. The subjects exhibiting considerable plantarflexor weakness all fell outside the +/- 1.96SD limit from 30-50% of foot length to toe-off while those exhibiting considerable dorsiflexor weakness fell outside the +/- 1.96SD limit between initial contact to 25-40% of foot length, and then surpassed the +/- 3SD limit after 55-80% of foot length. CONCLUSION: This analysis of gait-line asymmetry provides a reference database for young, healthy able-bodied subject populations for both further research and clinical gait analysis. This information is used to suggest non-pathological gait-line asymmetry pattern limits, and limits where detailed case analysis is warranted.