We will assay the relative concentration of citric acid cycle intermediates and those in the gluconeognic pathway. Assays can be run using samples from mice/organs that have also been infused with a ¹³C-labeled tracer, e.g. ¹³C-lactate. This strategy allows one to determine flux rates (via the ¹³C-labeling patterns) and identify points of control of a pathway, e.g. gluconeogenesis (via the relative concentration profiles).