ABSTRACT‐THIP (Lu 2–030) is pharmacologically a specific and potent GABA‐receptor‐agonist which in animal studies depresses monosynaptic and, to a smaller extent, polysynaptic spinal relflexes. 5 spastic patients were investigated by means of neurophysiological tests comparing the acute effect of a single oral dose of THIP (15–25 mg) to “the test situation without drug administration” with an interval of 2 days. The neurophysiological tests included quantitative studies of proprioceptive reflexes (T‐reflex, vibratory inhibition of the T‐reflex, resistance to passive movement of a spastic muscle and clonus) and of the flexor reflex (threshold and latency). The voluntary power was measured by a static technique. THIP clearly reduced the monosynaptic T‐reflex and reinforced vibratory inhibition of the IAmonosynaptic pathway. The flexor reflex threshold was slightly increased during THIP administration, but the changes were not significant. Flexor reflex latency, resistance to passive movement, clonus and voluntary p