Assay for citrovorum factor (NSC-3590) in the presence of methotrexate (NSC-740).

Treatment of certain malignancies with high-dose methotrexate/citrovorum factor rescue has recently been adopted as an effective regimen. A microbiologic assay capable of detecting citrovorum factor in the presence of massive amounts of methotrexate has been developed using a strain of Pediococcus cerevisiae resistant to methotrexate. The assay described in this paper is an inexpensive and rapid method of studying the distribution kinetics of citrovorum factor.