In the accompanying paper a sensitive and specific enzymatic method is described for the measurement of formiminoglutamic acid (1). In this paper data are presented on the application of this method for the assay of formiminoglutamic acid in the urine of a variety of patients.Formiminoglutamic acid is an intermediate in histidine metabolism, and requires tetrahydrofolic acid for its further metabolism. Previous results (2-5) have demonstrated that the urinary excretion of this compound is markedly increased in folic acid-deficient rats. Formiminoglutamic acid has also been reported (6, 7) in the urine of several patients receiving folic acid antagonists, although the techniques available for these studies were relatively cumbersome and inaccurate.Using the enzymatic procedure for the assay of formiminoglutamic acid, we have found that small amounts of this compound can often be detected in the urine of adults and children. A marked elevation in formiminoglutamic acid excretion was noted after amethopterin (methotrexate) therapy in children with acute leukemia. METHODS

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