This review cites evidence suggesting that the pedunculopontine nucleus (PPN), long known as a site of termination for basal ganglia outputs, is equivalent to the mesencephalic locomotor region (MLR), an area known to modulate spinal locomotion oscillators. The presence of cholinergic cells in this area also identifies it with the CH-5 cell group. In keeping with its cellular make-up, evidence is reviewed suggesting that the descending output of the PPN/MLR is cholinergic. This output may be under nigral GABAergic control which, in turn, may be under subthalamic influence. From various lines of evidence, it appears that the PPN/MLR receives elements of information from the motor cortex and basal ganglia centers involved in postural control. This area may be involved in the relay of information useful in the control of the center of gravity and other postural functions during locomotion. Pathological evidence is reviewed implicating basal ganglia afferents to the PPN/MLR (Parkinson's disease) and PPN/MLR efferents (Alzheimer's disease) in the deficits in locomotion observed in certain disorders.