The application of molecular biology to the study of the human erythrocyte membrane is presented in this report. We describe the strategy employed to clone DNA sequences encoding the membrane skeletal protein, protein 4.1. We demonstrate how these sequences may be utilized to deduce detailed structural and functional information about the 4.1 polypeptide. We also illustrate the use of cloned 4.1 DNA sequences as probes to explore the structural organization of the protein 4.1 gene in normal individuals and in patients with dysfunctional erythrocyte membranes. Ultimately it will be possible to generate a molecular description both of the structural proteins which constitute the membrane skeleton, and of the genetic mechanisms regulating their expression in erythroid and nonerythroid cells.