13C-labeled glucose is increasingly used in conjunction with magnetic resonance spectroscopy to measure rates of metabolic pathways in the brain in vivo. Most studies of human subjects have used intravenous infusions to administer the labeled compounds, but the procedure is cumbersome and can be uncomfortable for patients with neurological or psychiatric disorders. It may be possible to improve the practicality of the method by administering the glucose orally instead of intravenously. This report describes the performance and comparison of the oral and intravenous protocols in the same subjects. The conclusion is that oral administration does yield the same result as intravenous administration but with lower precision. That sensitivity of the oral protocol may be improved by several ways that are available today.