Recently discovered recurrent somatic mutations in the key metabolic enzymes IDH1 and IDH2 produce the aberrant oncometabolite 2-HG and contribute to malignant transformation of hematopoietic and glial cells. Two recent reports in Science describe the first IDH1 and IDH2 mutant-specific small-molecule inhibitors, which induce cell differentiation of myeloid leukemias and malignant gliomas.