Isoelectric focusing (IEF) of hemoglobin was compared to the classical chromatography of labeled globin chains for 22 antenatal diagnoses of hemoglobinopathies: 11 for beta thalassemia, and 11 for sickle cell disease. In all cases, the two methods gave identical results. The diagnosis was confirmed after birth or abortion. Three fetuses homozygous for beta thalassemia and one homozygous for sickle cell disease exhibited no Hb A by IEF, in contrast to normal fetuses or those heterozygous for one of the two hemoglobinopathies. In addition, blood samples obtained in other centers after abortion of 22 fetuses homozygous for beta + or beta 0 thalassemia exhibited no Hb A when analyzed by IEF. When Hb A was present, the respective proportions of Hb A and acetylated Hb F were determined by densitometry of the IEF gel. The Hb A/acetylated Hb F ratio obtained by IEF correlated well with the beta A/gamma ratio of globin chain synthesis, IEF requires 0.1 mg of unlabeled hemoglobin. It is performed in 90 min and several samples can be analyzed simultaneously. If present, maternal contamination of fetal blood must be eliminated by selective lysis of maternal (RBC) using the Orskov reaction. Improvements in this method to obtain suitable samples for IEF analysis are described.