High-resolution 1H-NMR of human urine. To examine the sensitivity of our instrumentation to obtain NMR spectra suitable for measurements of metabolic changes in response to varied sulfur amino acid intake, we obtained spectra from urine collected on 2 successive days without and with oral supplementation with 3 g Cys. Samples (300 μl) were mixed with 150 μl of 200 mM sodium phosphate buffer, pH 7.4, and 50 μl 2H2O prior to recording spectra with a Varian Inova 600 MHz spectrometer. Although the data are too preliminary to make conclusions, results demonstrate that spectral quality is similar to that reported by Nicholson and colleagues (23-25, 36-37) and suitable for detection of changes in concentrations of a large number of metabolites. In particular, peaks identified by Nicholson were present and several differences were evident between samples with supplemental Cys and without.