Twenty-eight outpatients with chronic severe lumbar pain participated in a double-blind comparative trial on the clinical efficacy of orally administered piroxicam and indomethacin. Half of the patients received indomethacin, 25 mg t.i.d.; the other half received piroxicam 20 mg in the morning and a placebo at lunchtime and before dinner for six weeks. The patients were examined four times at two-week intervals for their capability to do daily tasks and for total lumbar mobility, forward bending, raising of both legs straight and the subjective assessment of pain. Side effects were recorded on a questionnaire and with laboratory tests. The overall results of both groups were similar. Thus, piroxicam, 20 mg daily, matches indomethacin, 25 mg t.i.d., in the treatment of low back pain. The side effects were slight. Treatment with indomethacin was stopped in one case (erythema and conjunctivitis). In the piroxicam group diarrhea, constipation, and pain in the tongue were reported, whereas in the indomethacin group gastrointestinal irritation and tiredness were typical symptoms.