In our work, we investigate solutions of [ 15 N 2 ]-and [ 13 C, 15 N 2 ]-urea in various solution environments by observing changes in the compounds' zero-field NMR Jspectra. First, we demonstrate the influence of a protonexchange process on J-spectra by measuring [ 15 N 2 ]-urea and [ 13 C, 15 N 2 ]-urea in an aprotic solvent, dimethyl sulfoxide (DMSO), and a protic solvent, water (H 2 O). Since a proton-exchange rate in urea is both acid-and basecatalyzed, we also investigate aqueous solutions of [ 15 N 2 ]urea and [ 13 C, 15 N 2 ]-urea at various pH levels. The results are elucidated by zero-field NMR simulations of chemical exchange and nuclear spin dynamics using a simple theoretical model. [ 15 N 2 ]-urea is also measured in mixtures of H 2 O and D 2 O to study the effect of D nuclei on the zero-field J-spectra. The experimental results are supported by simulations taking into account the proportion of 1 H/D isotopologues of urea in solution. All spectral peaks, arising from J-coupling interactions ( 15 N-1 H, 15 N-D, and 1 H-D) in spin subsystems, are assigned by analyzing the energy-level structure of isotopologues using perturbation theory. Based on the presented results, we show straightforward ways to study complex biomolecules in ZULF NMR by taking advantage of the chemical-exchange process.