Outpatient dental anaesthesia was studied in August, 1961, to ascertain the techniques employed at a Teaching Hospital, observe the physiological response of patients and explore potential hazards (Volume Two, Part IV). Gas mixtures administered, pressures within the nose-piece, systolic blood pressure and brachial pulse were recorded. Analysis of results was restricted by the number of variables, but they suggest that hypoxia is undesirable, and they invite investigation into the recovery period and effects of surgical stimulation. Volume One describes preparatory studies. The literature is reviewed, preliminary clinical observations reported, problems posed and the overall plan of investigation stated (Part I). Assessment of resistance to gas flow through apparatus is related to its clinical application; delays in passage of gas mixtures through . breathing systems are analysed theoretically and experimentally; and the performance of the Walton Five dental anaesthetic machine used for the studies is assessed (Part IX). Apparatus employed for the clinical investigation was proved while studying the effects of expiratory resistance, oxygen and hypoxia on volunteers. Results suggest that hypoxia alters the response to pressure breathing. Speed of induction of anaesthesia is also related to the gas mixtures administered (Part m). Examination of alternative techniques involved the pharmacokinetics of inhalation anaesthetics, which is related here to outpatient anaesthesia. Two studies of nitrous oxide uptake produced erroneous results, but they defined the problems associated with the use of pneumotachography. Experiments using spirometry and bag-in-box systems demonstrated the uptake, distribution and elimination of nitrous oxide (Volume Two, Part V). Appendices include observations on a condenser-heat-exchanger, the lack of nitrous oxide uptake by the nose and naso-pharynx, the unsuitability of ballistocardiography for measurement of cardiac output, the jerkin plethysmograph, and recovery from outpatient anaesthesia. Volume Three contains reprints detailing the history of nitrous oxide and oxygen anaesthesia.