The purpose of this study was to compare the magnitude and duration of motoneuron inhibition occurring as a sequel to spinal manipulation or paraspinal and limb massage. The physiologic mechanisms involved in spinal manipulative therapy and massage therapy are largely unknown. One possible hypothesis is based upon the theory that these two distinct and different modalities may attenuate the activity of alpha motoneurons. Both modalities have been reported to produce short-term inhibition of motoneurons. Asymptomatic volunteers were randomly assigned to either a spinal manipulation, massage, or control group. Baseline tibial nerve H-reflex amplitudes were obtained prior to the application of either lumboscaral spinal manipulation or paralumbar and limb massage. Post-interventional H-reflex recordings were recorded immediately following the application of either modality. Spinal manipulation significantly (p < 0.05) attenuated alpha motoneuronal activity immediately post-therapy, as measured by the amplitude of the tibial nerve H-reflex. Massage subjects exhibited no significant reduction in motoneuronal activity immediately following administration. Spinal manipulation produced a transient attenuation of alpha motoneuronal excitability. Paraspinal and limb massage did not inhibit the motoneuron pool as measured immediately post-therapy. These findings support the supposition that spinal manipulation procedures lead to short-term inhibitory effects on motoneuron excitability to a greater magnitude than massage.