Ataxia-telangiectasia mutated (ATM) kinase regulates critical metabolic processes of B-cell lymphoid malignancies. Diffuse large B-cell lymphoma (DLBCL) is clinically a very aggressive tumor subtype. This study investigates the role of ATM in metabolism. Oxygen consumption rate measurements showed decreased respiration in DLBCL cells lacking ATM. MRS of hyperpolarized [1-13C]pyruvate in DLBCL line HLY that were either wild-type or had ATM knocked down showed increased conversion of hyperpolarized pyruvate to lactate in HLY cells lacking ATM. These results indicate that deregulation of mitochondrial structure/function due to ATM deficiency results in metabolic changes and may contribute to the development of cancer.