1H NMR Spectroscopy yields within a relatively short time useful information on the presence of endogenous metabolites in rat urine. The very intense water signal can be attenuated by lyophilizing the samples and reconstitution of the sample in deuterated water, followed by a saturation pulse of the residual HOD signal. When lyophilized urine samples are compared with non-lyophilized samples no apparent artefacts are introduced. Homonuclear J-resolved 2D- NMR spectroscopy is very well suited to obtain additional structural information. Using this approach an unknown urinary metabolite was identified as N-methyl-3-carboxamide 4-pyridone.<br>