Four neonates who presented with coma secondary to hyperammonaemia resulting in central respiratory failure were treated with peritoneal dialysis for between 16 and 120 hours. Underlying diseases were maple-syrup-urine disease, propionic acidaemia and citrullinaemia in two patients. Clinical improvement was observed in three patients within 16 to 72 hours after institution of peritoneal dialysis. Biochemical analysis revealed a rapid reduction in plasma concentration of leucine, isoleucine and valine as well as their alpha-keto-analogues in the infant suffering from maple-syrup-urine disease. Correction of ammonia, glycine, alanine and propionic acid concentrations was observed in the infant with propionic acidaemia 24-72 hours after institution of peritoneal dialysis. Severe hyperammonaemia (1,000-2,500mumol/l) in two infants with citrullinaemia before peritoneal dialysis was treated successfully in one infant; whereas the second infant showed no clinical improvement despite amelioration of biochemical parameters. Glucose-absorption from peritoneal dialysis solution was in the range of 216-441 mg/kg/h.