Experimental conditions were found for the preparation of stable fluorescent adducts of o-phthalaldehyde with glutathione and its metabolites: glutamine, glutamic and aspartic acids, gamma-glutamylglutamine and gamma-glutamylglutamylglutamine. The structure of the glutathione isoindole derivative obtained was confirmed by NMR studies. The procedure was applied to reversed-phase high-performance liquid chromatographic separation of the previous compounds. The method was extended to glutathione and "total glutathione" determinations.