We would like to thank Dr. Costedoat-Chalumeau and colleagues for their useful information related to the use of blood assays to monitor hydroxychloroquine concentrations in patients with systemic lupus erythematosus in France. We certainly see this assay as a useful measure of adherence. However, the majority of patients with rheumatoid arthritis receive other oral disease-modifying agents, most commonly methotrexate, and additional assays would be necessary. We believe adherence is a major determinant of therapeutic effectiveness and agree that any method that can further aid in its assessment should be evaluated in both research and clinical settings.