Recent studies have suggested that the subthalamic locomotor region (STLR) of the posterior hypothalamus is involved in modulating cardiorespiratory responses to feedback from contracting muscles. The purpose of this study was to determine whether neurons in this hypothalamic region alter their discharge frequency during contraction of hindlimb muscles. Stainless steel electrodes were used to record single-unit activity of STLR neurons during static and rhythmic contractions of hindlimb muscles in anesthetized cats. Recordings were also made from neurons in areas outside but surrounding the subthalamic locomotor region. Contraction of the triceps surae muscles was induced by stimulation of the peripheral cut ends of the L7 and S1 ventral roots. Both static and rhythmic contractions of the triceps surae evoked an increase in the discharge rate of the majority of the STLR cells studied. Two types of excitatory responses were observed: 1) abrupt increases in discharge frequency at the onset of muscular contraction and 2) a delayed more gradual increase in firing. Most of the cells that responded to muscular contraction could be activated by mechanical probing of the triceps surae muscles. However, the changes in discharge frequency were unrelated to changes in arterial pressure occurring during muscular contraction. Most of the neurons located outside the STLR were slightly inhibited by or did not respond to muscular contraction. Thus input from contracting muscles exerts predominantly an excitatory effect on neurons in the posterior hypothalamus. These results are consistent with other studies which have concluded that this hypothalamic site is involved in influencing the cardiorespiratory responses to muscular contraction.