The use of two-dimensional diffusion-edited total-correlation NMR spectroscopy (DETOCSY) to measure diffusion coefficients of molecules in biofluids is demonstrated. The method takes advantage of the increased peak dispersion in a two-dimensional spectrum and allows the measurement of diffusion coefficients of individual molecules in complex biofluid samples in a condition close to their natural state. The NMR spectra can be edited on the basis of diffusion coefficient, and hence, approximate molecular size and this provides a qualitative means of simplifying the spectra for assignment purposes. The use of two-dimensional DETOCSY NMR spectra increases the probability that the individual cross-peaks arise from single components and hence allows single-exponential fitting of the magnetic field gradient dependence of cross-peak volumes. Interpretation of the derived diffusion coefficients improves the NMR resonance assignment process in complex biofluid mixtures by giving additional information on the molecular size. The DETOCSY approach also provides information on small molecule-macromolecule interactions such as the binding of drugs or endogenous species to serum proteins such as albumin.