Our recently developed multiwavelength method for multi-component analysis of hemoglobin (Hb) derivatives (Clin Chem 1984;30:373-379) was adapted for routine use in the clinical chemical laboratory. The method was applied in 4066 determinations on blood specimens from patients awaiting major surgery (n = 3863) or visiting the outpatient department for pulmonary disease (n = 203). Mean total hemoglobin concentration was 141 (SD 14) g/L. The proportion of HbCO was slightly to moderately increased (1.5-10.0%) in 36.5% of all patients; in a few cases it was as high as 15%. Mean methemoglobin was 0.4% (SD 0.2%) in the surgical patients, but 1.5% (SD 0.8%) in the patients with pulmonary disease. In some patients of the latter group the proportion of methemoglobin amounted to 5%. Sulfhemoglobin was found less than 0.4% in all specimens. Interference by paraproteins and by increased concentrations of bilirubin and lipids in plasma was easily detected by means of the performance checks provided by the spectrophotometer (an HP 8451 UV/Vis). The method is equally suitable for measuring blood samples containing fetal hemoglobin.