Roles of certain inositol polyphosphates as intracellular signaling molecules are well known. However, the functions of more recently described inositol pyrophosphates, such as diphosphoinositol pentakisphosphate, which contain high-energy phosphate bonds, are less clear. Szijgyarto et al. (see the Perspective by Irvine and Denton) propose that these molecules may help to control metabolism and mitochondrial function. Yeasts engineered to lack inositol pyrophosphates grew more slowly. Such yeasts, and mouse embryo fibroblasts similarly depleted of inositol pyrophosphates, showed decreased mitochondrial function and increased glycolysis.