The present invention relates to a cDNA probe for the detection of the mRNA for human methenyltetrahydrofolate synthetase, which comprises the following nucleic acid sequence, Seq. Id. No. 1: ( * See Patent for Chemical Structure * ) PS or any functional analogs thereof wherein the hybridization of the probe and the mRNA for human methenyltetrahydrofolate synthetase is substantially preserved. The present invention also relates to a polyclonal antibody or an antigen-binding fragment thereof for the detection of the mRNA for human methenyltetrahydrofolate synthetase, wherein said antibody is raised against a protein segment aa100-112 H-Phe-Asp-Lys-His-Gly-Asn-Arg-Leu-Gly-Arg-Gly-Lys-OH, Seq. Id. No. 2 of human methenyltetrahydrofolate synthetase.