A new method, the cation exchange HPLC of haemoglobins, has been compared to the classical carboxymethyl cellulose (CMC) chromatography of globin chains for the prenatal diagnosis of beta thalassaemia and sickle cell disease. The two methods correlated highly. The HPLC procedure can use two independent and reliable means--optical density at 405 nm and radioactivity to determine the adult Hb/HbF+Fac ratio. The diagnosis is obtained in 15 min by cation exchange HPLC.