Metabolic pathways and bioenergetics were described in great detail over half a century ago, and during the past decade there has been a resurgence in integrating these cellular processes with other biological properties of the cell, including growth control, protein kinase cascade signaling, cell cycle division, and autophagy. Since many disease conditions are associated with altered metabolism and production of energy, it is important to develop new approaches to measure these cellular parameters. This chapter summarizes a new and exciting approach based on the Seahorse XF24 Extracelluar Flux analyzer, which takes real time measurements of oxidative phosphorylation and glycolysis in living cells. These bioenergetic profiles are then compared with steady-state levels of cellular ATP as measured by a luciferase assay.