Thirty patients with classical or definite rheumatoid arthritis were randomly divided into two groups of fifteen patients each of similar age, sex, duration and severity of disease, and medical treatment. All patients were treated once a day with bath salts heated to 35 degrees C for twenty minutes. Group I received Dead Sea bath salts and Group II, the control group, received sodium chloride (NaCl). The study was double-blind and of two weeks' duration. All patients were evaluated by one rheumatologist both before treatment, and two weeks later at the end of the treatment period. Follow-up evaluations were made one and three months after conclusion of the treatments. The clinical parameters evaluated included duration of morning stiffness, fifteen meter walk time, hand-grip strength, activities of daily living, circumference of proximal interphalangeal joints, number of active joints, Ritchie index and the patient's own assessment of disease activity. The laboratory parameters evaluated included erythrocyte sedimentation rate and serum levels of amyloid A, rheumatoid factor, sodium, potassium, calcium and magnesium. A statistically significant improvement (p less than 0.01 or p less than 0.05) was observed in Group I only, in most of the clinical parameters assessed. Maximal therapeutic effect was obtained at the end of the treatment and lasted up to one month.