Membrane-associated analogues of erythrocyte spectrin and ankyrin have been detected in nonerythroid cells by crossreaction with antibodies. Brain spectrin and a spectrin-binding domain of brain ankyrin have been purified and demonstrated to have all known functional activities of their erythrocyte counterparts. The nonerythroid forms of spectrin and ankyrin may have functions such as providing support for the lipid bilayer, mediating some types of actin-membrane interactions, and integrating membrane-spanning proteins with cytoplasmic structural proteins.