Twelve spastic patients with traumatic transverse myelopathies participated in a two-stage, double-blind crossover study using BA-34647 (a new experimental antispasticity drug by Ciba-Geigy) and placebo. Clinical measurements of spasticity were performed before, during and after each stage. Six patients had excellent results receiving a regimen of BA-34647 but not when receiving placebo. Four patients had fair-to-good results with both BA-34647 and placebo. One patient had no significant changes when receiving either drug or placebo, the effective dose not being reached due to excessive body weight. One patient had a shortened trial due to pain and diminished function caused by excessive spasticity. Abrupt changes in post-treatment symptomatology (increase in spasticity) occurred in all six patients who demonstrated excellent results and in all four patients with fair-to-good results. In each of these cases, the increase followed the discontinuation of BA-34647. In no case was there an increase of spasticity following discontinuation of placebo. The effectiveness of an antispasticity drug may be too subtle to be perceived subjectively and objectively. The rebound phenomenon is evidence that a pharmacodynamic effect, though minor, was present.