26 patients with osteoarthritis of the knees were randomly divided into 2 groups of 13 each with patients of similar ages, sex distribution and duration and severity of disease. All were treated with daily baths at 34-35 degrees C for 20 min. containing Dead Sea bath salts (Group I) or sodium chloride (Group II). The study was double-blind and of 2 weeks duration. Patients were evaluated by a rheumatologist before, at the end of treatment and 1 month later. Clinical parameters evaluated included index of severity of osteoarthritis, patient's assessment of disease severity, range of movement of knees, soft tissue swelling, effusion and crepitus. There was significant improvement in the index of severity of osteoarthritis at the end of the treatment in both groups (p < 0.01). 1 month later, in Group I the significance of the index was still p < 0.01, but p < 0.05 in Group II. Patient's assessment of improvement was significant only in Group I at the end of the treatment period (p < 0.01). There was no statistical improvement in either group in the other parameters assessed.