Intracellular recordings were carried out in extensor hindlimb motoneurons during L-DOPA-induced fictive locomotion from acute and chronically spinalized cats. It was demonstrated that motoneurons in chronic animals exhibited irregularly occurring, high frequency discharges within a given burst of a spike train, and sporadic membrane potential depolarizations and hyperpolarizations correlated with extensor and flexor nerve filament activity, respectively, during the locomotor cycle. In contrast, motoneurons recorded from acute cats demonstrated smooth membrane potential fluctuation and regularly occurring low frequency spike discharges. These results indicate that the pharmacologically activated central pattern generator (CPG) for locomotion in young adult chronic cats spinalized at two weeks of age produces disorganized locomotor-like patterns in the absence of sensory feedback. It is suggested that the above-mentioned characteristics of membrane potential fluctuations and spike discharges are not due to alterations in the motoneuron membrane properties, but instead are due to changes in the inputs to the motoneurons.