Over a 1-yr period, 102 patients with a clinical diagnosis of either medial or lateral epicondylitis (tennis elbow) or rotator cuff tendonitis were treated with topical applications of dimethyl sulfoxide (DMSO). A double-blind controlled study was carried out on these patients in the private practice of an orthopaedic surgeon to determine the efficacy of this material in the treatment of these two common clinical conditions. Beneficial effects were assessed with respect to improvement in pain, tenderness or swelling, and increase in the range of motion. Forty patients were treated for each of the two ailments; patients treated with the 70% DMSO aqueous solution did not receive any more beneficial effect from the drug than patients who received 5% DMSO aqueous placebo solution.