The accuracy of 2 ear oximeters (Hewlett-Packard 47201A and Biox IIA) was evaluated at rest and during exercise in 116 pulmonary patients. Ear oximetry measurements were compared with arterial oxygen saturation (SaO2) measured from simultaneous arterial blood samples. When used according to the manufacturer's instructions for stabilization during exercise testing, both oximeters demonstrated comparable accuracy in estimating arterial blood SaO2 both at rest and during exercise in these patients (95% confidence limits, 2 SEE = +/- 4 to 5%). The oximeters were more accurate in measuring a change in SaO2 from a previous reading (95% confidence limits, 2 SEE = +/- 2.5 to 3.5%). COHgb levels greater than 4% and dark skin pigmentation appeared to decrease the accuracy of ear oximetry measurements. Within the limitations of accuracy, both ear oximeters may be useful for clinical exercise testing in pulmonary patients.