A spectrophotometric scanning technique was used to quantitate hemoglobin concentrations in cardiac surgery patients and patients with other hemolytic disorders. 2. The fractional absorption of a portion of the 577 nm band of oxyhemoglobin was used in conjunction was used in conjunction with the absorption coefficient of oxyhemoglobin to relate absorption to plasma hemoblogin concentration. 3. The spectrophotometric scanning technique offers a rapid and accurate means of assessing plasma hemoglobin concentrations even in the presence of usual interferences by bilirubin, turbidity and methemalbumin.