Patients with Sjögren's syndrome were treated with vitamin A (100,000 U) daily during a two-week period. The vitamin treatment significantly elevated their ADCC and NK activity. The lymphocyte blast transformation, however was not noticeably changed. After the treatment, the retinyl-ester and retinol level of the plasma significantly increased as did the plasma level of vitamin E. The level of TBA reactive substances (malondialdehyde) in the plasma increased, whilst the glutathione peroxidase and catalase activity of erythrocytes decreased. The activity of the plasma glutathione peroxidase increased, but not significantly.