High dose methotrexate with leucovorin rescue has demonstrated activity in numerous malignancies. Although high dose methotrexate is generally well tolerated, unpredictable life-threatening toxicity can occur. For patients who have markedly delayed clearance of methotrexate secondary to renal dysfunction, therapeutic options are few and are of limited efficacy. Carboxypeptidase-G2 inactivates methotrexate by hydrolyzing its C-terminal glutamate residue. Carboxypeptidase-G2 could be used to rescue patients with renal dysfunction and delayed methotrexate excretion, as it provides an alternative to renal clearance as a route of elimination.