World-wide salinity and drought problems necessitate the understanding of biological adaptation to water deficit. Osmotic adjustment via organic solutes is a common strategy for organisms to deal with water deficit problems. Numerous water-soluble organic metabolites across several chemical classes are commonly utilized as osmolytes, including betaines, sulfonium and sulfonate compounds, amino acids, carbohydrates, and polyols. To deal with the complexity and variability in osmolyte composition, we have devised an analytical approach that combines high-resolution ({ }^{1} H) NMR and GLC to provide both structure identification and quantification of a broad spectrum of compounds. This combined approach also facilitated direct analyses of crude tissue extracts without extensive sample preparation, making it well-suited for a convenient screening of potential osmolytes. The structures of known osmolytes were confirmed from two-dimensional total correlation ({ }^{1}) H NMR spectra, which also yielded structural information about unknown compounds. Five each terrestrial plant and marine animal species were examined for 41 metabolites, including osmolyte candidates glycinebetaine, dimethylsulfoniopropionate, taurine, proline, glycine, asparagine, alanine, glutamine, glucose, and sucrose. The osmotic function of glycinebetaine, proline, asparagine, glutamine, glucose, and sucrose was also demonstrated in leaves of Distichlis spicata under different salinity treatments. 1983 Academic Press, Inc.