Application of the technique of gene mapping has made possible accurate assessment of the alpha thalassemia defect in cord blood samples obtained in a Sydney teaching hospital. Results showed a 5.2% incidence of the alpha+ thalassemia haplotype in the population being tested. Various hematological parameters such as hemoglobin, mean corpuscular hemoglobin, hemoglobin EPG pattern at pH 8.9 and the percentage of hemoglobin Bart's determined by elution at pH 6.7 were measured to assess which would be the most useful in diagnosis of alpha thalassemia at this time of life. The most consistent test proved to be hemoglobin EPG pattern at pH 8.9, and reasons for this are discussed.