In assigning values to fresh blood specimens used for calibrating automated blood cell analysers, haemoglobin concentration should be determined by the ICSH recommended hemiglobincyanide (HiCN) method. Errors in the reference method may be caused by inadequate blood collection, e.g. incorrect anticoagulation; inadequate dilution, e.g. use of inadequately calibrated pipettes; incomplete conversion of haemoglobins to HiCN, e.g. insufficient time for reactions to come to completion; during measurement, e.g. due to turbidity of the HiCN solution to be measured; or by transcription error. Readily available commercial reagent systems and secondary standards are compared with ICSH standards as to their compliance with these standards.