Field ionization mass spectrometry has been applied to multicomponent analysis of metabolites in human urine for the diagnosis of metabolic disorders, exemplified here by infectious hepatitis. The molecular weight profiles of carboxylic acids and of "neutral" metabolites in the urine of patients with infectious hepatitis were compared with those in urine of normals. The "neutral" metabolites showed 24 characteristic spectral differences in the range 68 to 215 atomic mass units, which provided correct diagnoses in 100% of the cases and a "diagnostic power" of unity. These results are even more encouraging than those obtained earlier with the acidic metabolites, where 11 mass numbers were found in the same mass range to be useful for correct diagnoses in 91% of the cases. The measurements were performed on urine samples preextracted on Amberlite XAD-2 columns. We used a quadrupole mass spectrometer interfaced with a multichannel analyzer for mass analyses.