This study evaluated arterial oxygen saturation (SaO2) over time in a randomly selected group of quadriplegic patients to assess whether clinical history prospectively correlated with profiles of oxygen saturation. In 16 stable male quadriplegic patients (C4-T5), we used pulse oximetry to measure SaO2 over a 24 hour period. Measured values of SaO2 were formatted into a cumulative frequency distribution of SaO2 over time. The cumulative SaO2 values from the quadriplegic patients were compared to SaO2 values in a control group of 12 age-matched healthy male subjects. Ten quadriplegic patients had SaO2 profiles comparable to the range observed in healthy subjects. Six quadriplegic patients had SaO2 profiles outside of the normative range. These 6 exhibited cyclic desaturations (> 4%) during periods of behaviorally-defined sleep, suggestive of sleep-disordered breathing. During wakefulness, however, their values of SaO2 were within the normative range. With respect to level of injury, age, time after injury, or medication use, there was no difference between the six 'hypoxic' quadriplegic patients and the 10 'normoxic' quadriplegic patients. Five of the 6 hypoxic patients had a positive medical history of snoring and increased daytime sleepiness, as compared to 6 of 10 normoxic patients who gave a similar history. We also performed polysomnographic studies in a subgroup of 7 quadriplegic patients. In this subgroup, sleep-disordered breathing was observed in 3 patients (AHI of 54/53/12 per hour, respectively). We conclude that in quadriplegic patients, in whom there is a low clinical suspicion for sleep-disordered breathing, there can occur significant decreases in SaO2 over time.