Lyophilized haemoglobin mixtures containing HbF and HbA were investigated as reference preparations in an interlaboratory collaborative study. Haemiglobincyanide mixtures in Drabkin's solution with 450–550 mg Hb/dl and 0.2–60% HbF were divided into samples of 10 ml, lyophilized in plastic containers and stored without vacuum at -20°C. After dissolution in 10 ml distilled water no change in spectral and electrophoretic properties or turbidity was observed; stable values for the total Hb concentration and HbF content were obtained over a period of over 2 years. These HbF standards can be prepared in reference laboratories and are recommended for quality control in HbF determination by alkali denaturation. For fetal haemoglobin determination the alkali denaturation technique of Betke, Marti and Schlicht is recommended for quantitation of HbF concentrations, at least between 2 and 40%. For values below 2% radioimmunoassay and for concentrations above 40% chromatographic procedures are more accurate. However, these methods will not be applicable in smaller haematological laboratories and in developing countries.