A comparison of level walking, on a walkway and on a treadmill, was performed using ten normal subjects. Motion about the knee was measured using a triaxial electrogoniometer, and foot-floor contact patterns were recorded by means of four foot switches attached to the sole of each shoe. On the walkway, the data were collected with the subject moving at a comfortable walking speed. The treadmill was then set at the average velocity obtained on the walkway. Knee joint rotation in the coronal and transverse planes did not change significantly between the walkway and the treadmill. In the sagittal plane, significant differences were found for total motion (p less than 0.01), swing phase motion (p less than 0.01), knee position at heel strike (p less than 0.05), and maximum swing phase extension (p less than 0.01). A comparison of the foot-floor contact patterns between walkway and treadmill ambulation revealed reduced heel contact time, with an increase in toe contact while on the treadmill. It was concluded that sagittal plane knee kinematics during level treadmill walking differ significantly from level overground walking.