The present invention provides methylenetetrahydrofolate reductase (MTHFR) inhibitors for use in selective inhibition of cancer cell growth in a mammal. These inhibitors can be a small molecule, an antisense oligonucleotide, a ribozyme, a triple helix forming oligonucleotide, an anti-MTHFR antibody or fragment thereof, an MTHFR mutant or a fragment of MTHFR. The present invention further provides nucleic acids encoding an inhibitor of MTHFR, and vectors comprising these nucleic acids. Also encompassed by the present invention are methods of using the MTHFR inhibitors for selective inhibition of cancer cell growth, and pharmaceutical compositions comprising the MTHFR inhibitors.