Arterial oxygen saturation was measured using pulse oximetry during induction of anaesthesia in 108 children aged 10 days--14 years. No restriction was placed on the method of induction. Oxygen saturation decreased to less than 90% in 29 children (26.8%) and less than 80% in seven children (6.4%). There was a significantly increased incidence of desaturation (to less than 90%) in children under one year of age, in those who had no premedication, in those who received only atropine as a premidicant and in children who were anxious or crying before intravenous induction. Oxygen saturation did not decrease below 90% in any child who received inhalational induction.