Random assessments of SaO2 were performed via pulse oximetry in 274 hospitalized non-ICU patients prescribed supplemental O2 in a large tertiary care university hospital. In 507 assessments performed in patients inspiring the prescribed O2, 426 were receiving excessive amounts of O2 to maintain a SaO2 > or = 92 percent. In 233 of these assessments, SaO2 was > or = 92 percent while breathing ambient air. In an additional 193 assessments, the concentration of inspired supplemental O2 was excessive to maintain a SaO2 > or = 92 percent. However, in 81 assessments performed in patients inspiring O2, the prescribed amount was insufficient to maintain SaO2 > or = 92 percent. These results indicate that O2 prescription in hospitalized non-ICU patients is excessive or not required in the majority of cases. Furthermore, routine use of pulse oximetry in hospitalized patients prescribed O2 may be useful in determining the continued need for supplemental O2 and adjusting the proper concentration needed to avoid hypoxemia.