A very severely retarded infant with a Dandy-Walker malformation was treated with valproate since the age of 6 months on account of infantile spasms. Three weeks after start of therapy dexamethasone was applied additionally because valproate was ineffective. Seventy-six days after initiation of valproate therapy the infant died with the clinical signs of fulminant valproate-associated hepatotoxicity despite the discontinuation of valproate. In combination with a febrile otitis media the child had been periodically restless and lethargic during the last week prior to liver coma. Activity of liver enzymes remained within normal limits up to two days before coma occurred. Analysis of valproate metabolites by gas chromatography/mass spectrometry yielded unusually high concentrations of the di-unsaturated metabolite E,E-2,3'-dien-valproate before and during liver failure. The concentrations of the main metabolites E-2-en-valproate und 3-keto-valproate remained within the usual range found during valproate therapy at steady state. The oxydation products 4-en-valproate and E-2,4-dien-valproate which are formed by alternative pathways and are considered to be hepatotoxic were detected in very low concentrations only. The application of carnitine, of antioxidants thought to improve the capacity of the free radical scavenger system (selen, vitamin E), and of N-acetylcysteine which can detoxify reactive drug metabolites could not prevent the fatal outcome.