Organic acidurias are a wide group of inherited metabolic diseases, sometimes with acute neonatal symptoms and life risk in the newborn. The clinical features are often not specific, but the pattern of urinary organic acids is diagnostic. Correct identification of metabolites and timely response are fundamental in this kind of work. Capillary gas chromatogaphy/mass spectrometry (GC/MS) is now the reference method for separation, identification and quantification of organic acids. The analysis of urinary extracts (extraction is described in the text) is routinely carried out on an H P 5988A GC/MS system. Mass spectra are compared with a dedicated library and full spectra retrieved from positive samples. A new and interesting perspective is opened by infrared spectroscopy coupled with capillary GC. The method allows remarkable informations, complementary to mass spectra, on molecular structure. The sensitivity of equipment used for infrared (HP 5965 IRD) permits the use of the same capillary columns and analytical conditions for both GC/MS and GC/Fourier transform infrared. Our preliminary results show that the infrared detector can be used in organic acid analysis and can be useful, too, in identification of unknown metabolites, when mass spectral data are not sufficient.