Twenty-seven investigators participated in a double-blind, parallel placebo-controlled trial of piroxicam involving 278 patients with acute low back pain. Therapy commenced within 48 hours of the injury and continued for 7 days. The drug was given in the recommended regimen of 40 mg once daily for the first 2 days and 20 mg once daily thereafter. After 3 days of therapy, piroxicam patients showed a statistically greater amount of pain relief in the lying (P less than 0.001), sitting (P less than 0.01), and standing (P less than 0.01) positions, but after 7 days the difference between treatments was no longer significant. After 1 week's therapy, however, the requirement for additional analgesic was significantly lower in the piroxicam group (P less than 0.05), and more piroxicam than placebo patients (42 versus 28) had returned to work (P less than 0.05). Toleration was excellent in most patients, with only 13% of the piroxicam and 17% of the placebo group reporting adverse effects of mainly mild or moderate severity. The profile of the adverse effects was similar for both treatments. Piroxicam can provide effective relief of acute low-back pain with good toleration; it should be considered for use in the initial treatment of this condition.