Endogenous metabolites have gained increasing interest over the past 5 years 
largely for their implications in diagnostic and pharmaceutical biomarker 
discovery. METLIN (http://metlin.scripps.edu), a freely accessible web-based 
data repository, has been developed to assist in a broad array of metabolite 
research and to facilitate metabolite identification through mass analysis. 
METLINincludes an annotated list of known metabolite structural information that 
is easily cross-correlated with its catalogue of high-resolution Fourier 
transform mass spectrometry (FTMS) spectra, tandem mass spectrometry (MS/MS) 
spectra, and LC/MS data.