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Hepatocyte transplantation (HT) has become an effective therapy for patients with metabolic inborn errors. We report the clinical outcome of four children with metabolic inborn errors that underwent HT, describing the cell infusion protocol and the metabolic outcome of transplanted patients. Cryopreserved hepatocytes were used as this allows scheduling of treatments. Functional competence (viability, cell attachment, major cytochrome P450 and UDP-glucuronosyltransferase 1A1 activities and urea synthesis) and microbiological safety of cell batches were assessed prior to clinical use. Four paediatric patients with liver metabolic diseases (ornithine transcarbamylase deficiency, OTC; Crigler-Najjar syndrome, CNI; glycogen storage disease Ia GSD Ia; and tyrosinaemia type I, TYR-I) underwent HT. Indication for HT was based on severity of disease, deterioration of quality of life and benefits for the patients, with the ultimate goal to improve their clinical status whenever liver transplantation (LT) was not indicated or to bridge LT. Cells were infused into the portal vein while monitoring portal flow. The protocol included antibiotic prophylaxis and immunosuppressant therapy. After HT, analytical data on the disease were obtained. The OTC-deficient patient showed a sustained decrease in plasma ammonia levels and increased urea production after HT. Further cell infusions could not be administered given a fatal nosocomial fungus sepsis two weeks after the last HT. The CNI and GSD Ia patients improved their clinical status after HT. They displayed reduced serum bilirubin levels (by ca. 50%) and absence of hypoglycaemic episodes, respectively. In both cases the HT contributed to stabilise their clinical status as LT was not indicated. In the infant with TYR-I, HT stabilised temporarily the biochemical parameters, resulting in the amelioration of his clinical status while diagnosis of the disease was unequivocally confirmed by full gene sequencing. In this patient, HT served as a bridge therapy to LT.