A double-blind trial was carried out in 40 patients with various inflammatory syndromes to assess the effectiveness and tolerance of protacine, a new non-steroidal anti-inflammatory agent. Twenty in-patients with arthritis or arthrosis localized to the hip or knee were given either 150 mg protacine or 50 mg indomethacin 3-times daily, orally, for 10 days on average. Twenty patients (10 in-patients and 10 out-patients) with inflammatory disorders in different locations were given either 150 mg protacine or 200 mg oxyphenbutazone, 3-times daily, orally, for 18 days on average. Assessments were made before and after treatment of pain severity and, in the first group, of joint mobility measured in degrees of joint movement. Laboratory tests were also carried out. Side-effects were scored and reported. Except for indomethacin in the case of joint mobility, all three drugs resulted in significant improvement in the conditions tested. There were no changes in the laboratory parameters tested and only 1 patient on protacine and 1 on oxyphenbutazone reported side-effects, namely slight gastric discomfort and moderate headache, respectively. Two patients on indomethacin dropped out because of severe epigastric pain, and 2 others reported severe epigastric pain but treatment was continued. These preliminary results suggest that protacine may be at least as effective and better tolerated than indomethacin and oxyphenbutazone in such patients with acute and chronic inflammatory disorders.