The Swedish Society of Anaesthetists conducted a nationwide retrospective survey of clinical experience with extradural and intrathecal opiates. Special interest was focused on the frequency and type of ventilatory depression. The questionnaire was answered by 84 of 93 departments (90%). Up to May 1981 extradural morphine had been given to approximately 6000-9150 patients, extradural pethidine to 220-450 and intrathecal morphine to 90-150 patients. Ventilatory depression requiring treatment with naloxone was reported in 23 patients treated with extradural morphine (0.25-0.40%) and in six given intrathecal morphine (4-7%). In 22 patients the administration of extradural morphine was considered as a major contributory factor for the occurrence of ventilatory depression. Only two of these 22 patients experienced ventilatory depression later than 6 h after the last dose of opiates (S.C., i.m., i.v. or extradural). Patients aged 70 yr or more, those receiving thoracic extradural puncture and those with reduced ventilatory capacity seemed to be overrepresented.