Metabolism of halothane was studied in nine children receiving daily halothane anaesthetics (from 10 up to a maximum of 31) over periods of two to seven weeks. Serum bromide concentrations never exceeded 3.5 mmol/l, a concentration below the toxic threshold. Repeated halothane anaesthetics at short intervals did not induce the reductive metabolism of halothane as assessed by 2-chloro-1,1,1-trifluoroethane (CTF) in the expired breath. One patient developed viral hepatitis A during the course of anaesthetic administration; this patient was the only one whose serum bromide concentrations fell substantially and whose exhaled CTF concentration increased as more anaesthetics were administered.