Influence of methotrexate on results by three methods for determining protein in cerebrospinal fluid

Because high intravenous and intrathecal doses of methotrexate are used in treatment for various neoplasms, this drug can reach high concentrations in cerebrospinal fluid. At those encountered clinically, it produced significant positive interference with values for cerebrospinal fluid protein as determined with the du Pont aca. A small interference was found with the Folin-Lowry method, and virtually no interference with an automated immunochemical procedure.