Defects in the branched chain amino acid metabolism are the most common forms of organic aciduria. Two thirds of the cases manifest themselves during the neonatal period, most of them with an acute onset. Prompt diagnosis of organic acidurias is a task of the pediatrician and the neonatologist and depends on their early identification of children with suspect clinical symptoms. Between 1984 and 1987 9 patients presented with an organic aciduria at the Pediatric Department of the University of Innsbruck, 7 of them were neonates. 4 of these 7 children had a defect in the branched chain amino acid metabolism, 3 with propionic acidemia, one with maple syrup urine disease. The remaining 3 children presented with lactic aciduria. In all our patients diagnosis was performed by combined gas chromatography and mass spectrometry of spontaneous urine samples. Diagnostic procedures and therapeutic measures applied in the acute metabolic crisis are presented. Continuous arteriovenous hemofiltration has been found to be an efficient method for eliminating toxic metabolites in intractable metabolic acidosis.