Transgenic animals are utilized to produce therapeutically important protein products, such as tissue plasminogen activator, factor IX and α1-antitrypsin. Additionally, transgenic technology affords the opportunity to create animal models to study the pathophysiology of genetic diseases under controlled experimental conditions. Transgenic techniques provide a powerful approach for further studies of the structural and functional implications of mutated hemoglobins, the pathological consequences of abnormal hemoglobins, and the prospect of producing hemoglobins to be utilized as blood substitutes. Moreover, investigations utilizing transgenic approaches allow an increased understanding of expression and regulation of globin genes, which is important for the development of animal models and treatment of hemoglobinopathies. Such investigations of hemoglobin diseases also provide a basis for further refinement of techniques necessary for targeted insertion of genes into human cells, which increases the prospects of gene therapy as the ultimate cure for certain genetic disorders. © 1994, Elsevier Inc. All rights reserved.