In the November Nature Biotechnology Fiehn et al. offer an alternative to the profiling of messenger RNA and protein levels. They use gas chromatography coupled to mass spectrometry (GC/MS) to assay the relative levels of 326 small compounds from a plant leaf extract (Nat Biotech 2000, 18:1157-1161). A simple methanol extraction is followed by derivitization to increase metabolite stability and volatility. Approximately half of the chromatographed compounds can be identified based on retention times and mass spectra; these results can be viewed on the accompanying website. Biological variability (of approximately 40%) is in clear excess of variability inherent to the method (about 8%). Principal component analysis allows metabolite profiles from plants of a particular genetic background or with a particular mutation to be clustered. Mutation of a single gene causes many changes, most of them unexplained. Metabolite profiles may be useful to address public concerns about the safety of genetically modified food.