When a treadmill accelerates continuously, the walk-run transition has generally been assumed to occur at the instant when a flight phase is first observed, while the run-walk transition has been assumed to occur at the instant of the first double support period. There is no theoretical or empirical evidence to suggest that gait transitions occur at the instant of these events, nor even whether transitions are abrupt events. The purpose of this study was to determine whether the gait transitions during human locomotion occur abruptly, and if so, to determine the instant during a stride at which a transition occurs. The time history of the vertical velocity of the hip (v_hip) and the angular velocity of the ankle (ω_ankle) were compared between constant speed strides (walking or running) and strides at and near the walk-run and run-walk transitions to determine if and when the transition strides resemble the stride of the corresponding constant speed strides. For both the walk-run and run-walk transitions, the stride prior to the transition resembled the original gait pattern, while the stride following the transition resembled the new gait pattern. The transition stride, however, did not resemble either a walking or a running stride during either of the transition directions. It was concluded that gait transitions are initiated at about midstance of the transition stride, but the transition is not completed until after an adjustment period of between one step and one stride. Thus, gait transitions are not abrupt events during human locomotion.