High-resolution MS/MS analyses reveal that most metabolites in humans, mice, and C. elegans are unidentified. Recent discoveries of ascarosides, steroids, and other compounds in C. elegans are just the beginning. Humans and C. elegans likely have more metabolites than genes, with many yet to be identified. The Shroeder Lab studies comparative metabolomics using mass spectrometry and NMR spectroscopy to identify biosynthesis-regulated metabolites and aid in the functional annotation of new metabolites. This approach has led to the discovery of hundreds of new metabolites in C. elegans and other nematodes, with unexpected structures and biological activities. Research is ongoing to understand their biosynthesis and role in regulating endocrine signaling.