This study was initiated to determine if the absorbance spectra of hemoglobins from nonhuman species were sufficiently different from those of human hemoglobin to affect the applicability of pulse oximetry to common domestic species. Hemoglobin was isolated from the blood of humans, dogs, cats, horses, cows, and pigs. The millimolar extinction coefficients for oxygenated and deoxygenated hemoglobin samples were determined over the wavelength range of 600 to 1000 nm. Minor differences in the absorbance of both oxyhemoglobin and deoxyhemoglobin were found between human hemoglobin and that of the dog, cat, horse, cow, and pig. However, correction for the presence of methemoglobin, the effects of light scattering by impurities in the solution, and technical error rendered these differences statistically insignificant. The results of this study suggest that the spectral properties of canine, feline, equine, bovine, and porcine hemoglobin do not differ significantly from that of human hemoglobin and should not be a limiting factor in the application of pulse oximeters that are based on human algorithms to animal species.