Thiocolchicoside is a muscle relaxant which, due to its mainly spinal GABA-agonist activity, is used by the oral and intramuscular routes in the ambulatory treatment of painful contracture of the skeletal muscles. The effectiveness and acceptability of this drug in the treatment of acute low-back pain were evaluated in a multicentre, randomized, double-blind, drug versus placebo trial involving 98 patients. The effectiveness of thiocolchicoside was assessed on the following criteria: patients' overall opinion, pain intensity, number of analgesic tablets taken, vertebral rigidity and ability to resume ordinary daily tasks. The results obtained showed that thiocolchicoside significantly improves the principal criterion by the second day of treatment and the other criteria within 5 days.