This investigation assessed the mechanisms of Tetrazepam action on spasticity using a battery of electromyographic methods. Thirty patients with post-stroke spastic hemiparesis treated with Tetrazepam took part in the investigation. A questionnaire for assessment of subjective improvement after treatment used a 5-point scale. The 5-point scales were used to assess muscle tone, muscle strength and tendon reflexes. A battery of electromyographic methods was used to analyse different mechanisms of spasticity: for alpha-motoneuron activity--the F-wave parameters; for gamma-motoneuron activity--the TA/H amplitude ratio; for presynaptic inhibition--the ratio of H-reflex maximal amplitudes before and after vibration on the Achilles tendon (Hvibr/Hmax); for common interneuron activity--the flexor reflex parameters. Our results revealed that Tetrazepam reduces tone in spastic muscles and has a slight effect on tendon hyperreflexia. It has no influence on muscle strength, Babinski sign and ankle clonus. Tetrazepam acts by decreasing motoneurone activity and increasing presynaptic inhibition.