Abstract Stable isotope dilution assays for the quantification of pantothenic acid and folates in foods by using four-fold labeled isotopomers of the vitamins as internal standards (IS) were developed. The use of labeled IS enabled to exactly correct losses during cleanup and derivatization. Pantothenic acid and its labeled isotopomer were detected as trimethylsilyl derivatives by gas chromatography–mass spectrometry. In starch a detection limit of 44 μg/kg, an intrasample relative standard deviation of 6.7% and recovery values ranging between 97.5 and 99.4% were determined. Total pantothenic acid contents were analyzed in rice, milk powder and apple juice after enzymatic hydrolysis of the vitamin's conjugates, free pantothenic acid was quantified by omitting enzyme treatment. Almost all results were found to be in good agreement with the literature data. For quantification of folates, four-fold deuterium labeled folic acid was prepared in a first step and used as starting compound for the syntheses of tetrahydrofolate (H 4 folate), 5-methyl-H 4 folate, and 5-formyl-H 4 folate. These compounds were added as IS to food extracts in which pteroylpolyglutamates were subsequently enzy-matically deconjugated. After separation by high-performance liquid chromato-graphy, folates and their isotopomers were detected by two-dimensional mass spectrometry using electrospray ionization. The results revealed good agreement with reported contents in spinach, whereas some differences to the published data for broccoli were found.