Twenty ASA I or II patients were studied to assess the safety of oxygenation for 4 min prior to intubing, so as to prevent the hypoxaemia related to tracheal intubation. The arterialized capillary blood saturation (Spo2) was continuously monitored with a pulse oximeter Nellcor 100 equipped with a finger probe. Patients spontaneously breathed oxygen (FIO2 = 1) while anaesthesia was induced with pancuronium bromide, thiopentone and fentanyl. Following apnoea, ventilation was manually controlled during 4 min (FIO2 = 1). The values of Spo2 were recorded before induction, at the end of the 4 min oxygenation period and after 5 min of apnoea. An arterial blood sample was withdrawn at the end of apnoea and analysed immediately using an OSM 2b hemoximeter. Apnoea was interrupted in case of desaturation below 95%, new arrhythmia or haemodynamic instability (blood pressure +/- 20% of control value). Mean saturation (+/- SD) before oxygenation was 98.6 +/- 1.35%. After oxygenating for 4 min, all the Spo2 reached 100%. After the 5 min apnoea period, no saturation was below 95% (mean +/- SD = 98.89 +/- 1.66); at this time, Sao2 and Spo2 did not significantly differ (p less than 0.001). In one case, apnoea had to be interrupted, because of the occurrence of arrhythmias, unrelated to a blood gas disorder (PaO2 = 225 mmHg; Paco2 = 34 mmHg; SaO2 = 100%; pH = 7.44). This study confirmed the efficacy and safety of oxygenating for 4 min before intubation.(ABSTRACT TRUNCATED AT 250 WORDS)