This study evaluated the accuracy of pulse oximetry measured by a modified laryngeal mask airway (LMA). Ten anaesthetized patients (ASA I-II, aged 18-45) undergoing elective knee arthroscopies (mean-duration 40 min) were studied. A transmission pulse oximeter probe/sound OHMEDA was attached on the back of LMA (sizes 4 and 5) in an area in contact with the floor of the laryngeal part of the pharynx. Pharyngeal pulse oximetry as well as LMA cuff pressure were monitored and recorded every 5 min from the time of insertion (T0) to removal (T8) and were compared to simultaneous finger pulse oximeter readings. At T2 the cuff was over-inflated to obtain a 100 cm H2O intracuff pressure. At T3 the cuff pressure was decreased at 60 cm H2O. Pharyngeal pulse oximetry correlated with finger pulse oximetry throughout the study and was not effected by over-inflation of the LMA. This modification of the LMA provides an accurate method of measuring pulse oximetry which may be of use in a variety of circumstances.