Spectrin and spectrin-like proteins were found in almost all animal and protozoan cells. Moreover, several reports indicate their presence also in plants. We found that polypeptides reacting with anti-spectrin antibodies are also present in bacteria such as Escherichia coli and Halobacterium salinarium. In Escherichia coli only polypeptide(s) reacting with antibodies directed against a- subunit could be detected while in Halobacterium salinarium polypeptides reactive with antibodies directed against both subunits (α and β) were found. Our data may suggest a presence of spectrin-related polypeptides in early stages of evolution.