Caenorhabditis elegans is one of the best-studied animals in science. Despite this, metabolomic studies in C. elegans have only recently become active areas of research. The Isotopic Ratio Outlier Analysis (IROA) protocol uses 13C-isotopic signatures to identify and to quantitate metabolites (Figure 1). It reduces error introduced during sample preparation and analysis, including ionization suppression by the use of IROA standards. The marriage of IROA and high-resolution accurate mass (HRAM) LC/MS/MS with C. elegans metabolomics allows experiments which assess the biological response to stresses or stimuli. These experiments would conventionally be difficult due to interferences by metabolites of unlabeled organisms. With IROA labeling and HRAM detection, metabolites can be distinguished in an untargeted manner, quantitated and unambiguously identified to their chemical formulas.