The ring-infected erythrocyte surface antigen (RESA) associates with spectrin in the erythrocyte membrane (Foley, M., Tilley, L., Sawyer, W. H., and Anders, R. F., 1991, Mol. Biochem. Parasitol. 46, 137-148). In this study, we have used deletion mutagenesis combined with an in vitro binding assay to identify a region of the RESA polypeptide that is involved in the attachment of this parasite protein to the host membrane skeleton. It was found that the tandem repeat sequences of RESA do not appear to be involved in the association of this protein with the erythrocyte membrane and that large deletions of the N-terminal region of RESA did not affect binding. The membrane-binding domain has been mapped to a 48-amino-acid region of RESA located between the two blocks of repetitive amino acid sequence. This binding domain does not overlap the region of RESA that shares homology with the Escherichia coli molecular chaperone, DnaJ. Identification of the amino acid sequence which is critical for the binding of RESA to erythrocyte spectrin may provide important clues to the functional consequences of RESA attachment to the host membrane.