Localized 31P NMR spectroscopy was used to study the developing human liver in three neonates and one infant, all with neonatal intracranial problems, but normal liver function. A prominent resonance was present in the phosphomonoester (PME) region of the spectrum of the neonates; the PME/ATP ratio was 1.0 ± 0.4 (repetition time 1 s), compared to the mean adult liver value of 0.2 ± 0.1. The saturation factor of PME in the neonates was large, indicating that the increase in PME/ATP reflected an increase in relative PME concentration. The chemical shift of the PME peak in the neonatal liver (6.8 ± 0.1) was similar to that found in neonatal brain, suggesting that phosphorylethanolamine may be a major constituent. The phosphodiester (PDE)/ATP ratio in these patients (0.4 ± 0.1) was decreased compared with the mean adult value (1.3 ± 0.2), and the saturation factor of PDE was small. The results from the infant were different from both the neonates and adults; PME/ATP was decreased compared to the neonates, but increased compared to adults. The saturation factor of PDE was increased compared to neonates. The biochemical implications of the observed changes in PME and PDE in paediatric liver are discussed in relation to membrane turnover.