The authors note that despite a few reports in the literature indicating that saliva lithium levels could adequately replace serum determinations in monitoring patients being treated with lithium salts, this procedure has not received much clinical application. A study of 20 patients investigated correlations between serum and mixed saliva and parotid fluid lithium levels and documented the reliability of this procedure. The authors suggest that an individual patient's ratio of serum to saliva concentrations should be calculated and used as a constant in the determinations. Patients can collect saliva samples and send them to the laboratory prior to their visits, decreasing the facility's sample collection costs and the patients' inconvenience and discomfort.