In veterinary medicine, PCV determined by centrifugation of blood in a microhematocrit tube is the most common clinical test used to initially assess and monitor anemic and polycythemic animals. In contrast, blood hemoglobin (Hb) concentration, rather than PCV, is generally determined in human patients. One automated system photometrically measures blood Hb concentration after conversion of Hb to azide methemoglobin without dilution and was found to be a simple and accurate instrument for use in human medicine. We evaluated the system for its accuracy in measuring blood Hb concentration in animals by comparing it with standard techniques and for its suitability in veterinary practice. Blood samples, anticoagulated with potassium EDTA, from 78 healthy animals (33 dogs, 17 cats, 13 horses, and 15 cows) and 58 dogs and 4 cats with various blood abnormalities (10 anemia, 11 polycythemia, 21 lipemia, 16 leukocytosis, and 6 icterus) were analyzed. In all species, blood Hb concentration of healthy animals determined by the system was comparable to that measured by standard cyanmethemoglobin methods (ie, an automated counter; rI = 0.987 to 0.998 and a hemoglobin kit, rI = 0.946 to 0.993). The aforementioned system also yielded similar values to those obtained by use of standard methods in anemic, polycythemic, and icteric dogs and cats. Moreover, the system reads the absorbance at 2 wavelengths to correct for turbidity, and therefore, accurately measured Hb concentration in blood samples with severe lipemia (triglycerides concentration > 500 mg/dl) and marked leukocytosis (> 50,000 WBC/microliter), whereas other standard Hb techniques are known to give falsely high results.(ABSTRACT TRUNCATED AT 250 WORDS)