Stimulation electrodes were implanted in 63 rats at a total of 208 sites in the diencephalon and midbrain. The sites were tested for elicited forward locomotion, i.e., alternate stepping of the forelimbs and/or hindlimbs, while the rats stood on a treadmill belt in a 27 X 9 X 24-cm chamber. Current levels of 50-300 microA and pulse frequencies of 50, 100 and 154 Hz were presented as single 5-sec trains and as 20 repetitive trains of 1-sec duration with a 3-sec intertrain interval. Locomotion was elicited with low current (50 or 100 microA) single trains at 28% of the sites. Of the regions sufficiently well sampled to warrent comparisons, two showed high densities of locomotion-positive sites with single low current trains. They were the medial hypothalamus (the dorsomedial and the posterior nuclei) and the ventral tegmental area. The medial forebrain bundle and the zona incerta were generally positive but many sites in these regions required repetitive trains. Among the regions with few locomotion-positive sites were the subthalamic nucleus, the fields of Forel and the habenular complex. In the dorsal midbrain, in and around the central gray, low current single trains elicited leaping. The results are discussed in terms of the existence of a delimited subthalamic locomotor region and a ventral midbrain locomotor system independent of a dorsal midbrain system.