The effect of eperisone-HCI on the spinal stretch reflex was investigated in cats anesthetized with urethane-chloralose. The reflex activity, elicited by muscle stretches, was recorded from the split ventral root and analyzed using a crosscorrelation histogram between the motoneuronal spikes and muscle stretches. Eperisone-HCI was intravenously applied at a dose of 5 mg/kg. It was found that eperisone weakly inhibited the reflex activity of tonic motoneurons (approximately 30%), and that of the phasic ones was either moderately (approximately 70%) or completely (100%) inhibited by eperisone. The cross-correlation analysis suggested that the membrane potentials of both tonic and phasic motoneurons are equally lowered by eperisone or that monosyn.p tic transmission from primary afferents of muscle spindles to motoneurons is inhibited by eperisone.