Children with certain inherited metabolic disorders excrete diagnostic acylcarnitines which reflect unusual acyl-CoA intermediates accumulating at the metabolic block (Roe et at., 1986). These metabolites can be detected in urine, if their concentration exceeds about 50nmol/ml, by fast atom bombardment mass spectrometry (FAB-MS). By applying tandem mass spectrometry (MS/MS) it is possible to lower the detection limit to 1 nmot/ml in urine or blood (Millington et al., 1989). We investigated the potential of this new technique to identify metabolic disorders from small blood samples and from blood spots taken for existing neonatal screening tests (Guthrie cards). The preliminary results are presented here. These children were not receiving L-carnitine supplements at the time of sampling. A sample of umbilical cord blood from a normal child was employed as a control. The original Guthrie cards were recovered for children with subsequently confirmed diagnoses of MCAD deficiency and propionic acidaemia, recently diagnosed at Duke Medical Center. Controls were obtained from the North Carolina State laboratory. To determine recovery, normal blood was spiked appropriately with known concentrations of specific acylcarnitines and internal standards after spotting onto and recovery from Guthrie cards, as described by Millington et al. (1989). 321

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