Four cases of abnormal metabolic patterns which were obtained from three infantile patients and one adult on valproate (valproic acid; 2-n-propyl-pentanoic acid) therapy are reported. Serum levels of valproate and 15 metabolites were measured by gas chromatography/mass spectrometry. A mentally retarded, 11-month-old boy developed an extremely altered metabolic profile after having been treated with valproate polytherapy for 3 months. The altered pattern included strongly elevated serum levels of the 4-ene as well as of the omega-/omega1-metabolites, with the beta-metabolites (2-ene; 2,3'-diene) being diminished. Two samples obtained previously had shown a common pattern. The infant died 3 weeks after the last sample had been taken. Two boys of the same age showed similar but less intense deviations in their metabolic profiles at the onset of valproate therapy. Within a few weeks they approached, in a step-wise fashion, the average pattern common for children under 3 years of age. The striking alterations were paralleled by the metabolic profiles of an adult patient who suffered from intrahepatic metastasis and renal insufficiency. From the close resemblance of the abnormal metabolic patterns it was concluded that liver dysfunction results in alteration of the whole metabolic system. Regular inspection of the entire profile of an individual might help to recognize conspicuous alterations in time to avoid severe side effects.