BACKGROUND One of the most frequent complications in the immediate post-operation period is the fall in arterial oxygen saturation due to different factors, outstanding of which is the time that the patient remains disconnected from the oxygen supply during transport from the operation site to the recovery ward. The aim of the present paper is to measure the proportion of arterial desaturation in patients who arrive in the recovery room proceeding from the operation site without oxygen provision during transport. MATERIAL AND METHOD The study was made with a sample of 208 cases corresponding to the patients who underwent operations in the period from March 20th to April 19th 2000. Saturation was measured by pulse oximeter at the moment of arrival in the recovery unit prior to the provision of oxygen. Patients were classified in four groups according to average saturation and they were grouped by ASA and the anaesthetic technique employed. The statistical treatment was carried out with Student's t and variance analysis. RESULTS The sixty three per cent of patients showed a saturation of > or =95%; 26.4% slight desaturation; 6.3% moderate desaturation and 1% severe desaturation. The average of saturation of the ASA III patients showed significant differences with the ASA II and ASA I patients (p=0.004). Patients with general anaesthetic showed a desaturation with significant differences with respect to the other anaesthetic techniques employed (p<0.05). CONCLUSIONS ASA III patients and those subjected to general anaesthetic require oxygen provision during transport from the operation site to the recovery ward.