To assess the clinical applicability of pulse oximetry in the intensive care setting, a comparison was made of arterial hemoglobin saturation values determined by in vitro oximetry (SaO2) and pulse oximetry (SpO2) in 21 critically ill dogs. Single SaO2 measurements were compared to simultaneously obtained SpO2 readings. The correlation between these two methods was statistically significant (r = 0.8944, p = 0.0001). In addition, heart rates read by the pulse oximeter were compared to simultaneously obtained electrocardiograms (ECG). The correlation between these two methods was statistically significant (r = 0.9966, p = 0.0001). The pulse oximeter was easy to use, and recorded trends in oxygenation virtually instantaneously. Pulse oximetry appears to be an accurate and practical technique for the continuous non-invasive monitoring of oxygenation in critically ill dogs in the intensive care unit.