The preparation, storage and use of a hemolyzed blood product for simultaneous pH, pCO2 and pO2 [CO2 and O2 tension] quality control is described. Tonometry of the blood product with 2 O2 and 2 CO2 concentrations resulted in consistent and reproducible values during 38 wk. The resulting pH values were consistent and reproducible, demonstrating the metabolic acid-base stability of the blood product. The proper preparation, storage and use of the product results in consistent, reproducible and economical quality control for pH, pCO2 and pO2 blood measurements.