There are several metabolites that cannot be detected with conventional MRS methods, but which have aromatic protons that resonate in the downfield (>4.7 ppm) proton spectrum, including adenosine triphosphate (ATP), carnosine, nicotinamide adenine dinucleotide (NAD+), and tryptophan. These metabolites have important roles in the health and disease of tissue. Though downfield spectroscopic methods have recently been developed to detect these metabolites, their magnetic relaxation properties have remained unexplored. Quantification of parameters such as T1 and T2 are necessary for metabolite quantification and to facilitate protocol optimization. Additionally, magnetization exchange between metabolites and tissue water may reflect aspects of the microenvironment such as metabolite binding. Therefore, the objective of this work was to use downfield spectroscopic techniques to measure the in vivo relaxation properties of metabolites in skeletal muscle and the brain at 7 T in humans. I first measured the effect of cross-relaxation with water on T1 relaxation of adenosine and carnosine in calf muscle with inversion recovery experiments utilizing spectrally-selective single-voxel spectroscopy. Additionally, the cross-relaxation rate of these metabolites with water was explicitly quantified using a 2-spin model. It was determined that adenosine has a much stronger cross-relaxation effect and faster rate of cross-relaxation than carnosine. In the second experiment, the sequence was modified to enhance the signal-to-noise ratio of low concentration metabolites. The T1 and T2 relaxation times of NAD+ were measured in the brain and subsequently used as correction factors for NAD+ quantification. Finally, the cross-relaxation and chemical exchange rates were quantified for NAD+ and tryptophan, respectively, in the brain using saturation recovery experiments and the 2-spin model. Tryptophan was found to have a faster rate of magnetization exchange than NAD+ in vivo. The significance of this work is the quantification of several relaxation properties of downfield metabolites at 7 T for the first time in human tissue in vivo. These results will aid in the design of future studies of downfield metabolites, and these relaxation properties may serve as biomarkers of disease which reflect the cellular microenvironment.