We have identified four novel repeats and two domains in cell surface proteins encoded by the Methanosarcina acetivorans genome and in some archaeal and bacterial genomes. The repeats correspond to a certain number of amino acid residues present in tandem in a protein sequence and each repeat is characterized by conserved sequence motifs. These correspond to: (a) a 42 amino acid (aa) residue RIVW repeat; (b) a 45 aa residue LGxL repeat; (c) a 42 aa residue LVIVD repeat; and (d) a 54 aa residue LGFP repeat. The domains correspond to a certain number of aa residues in a protein sequence that do not comprise internal repeats. These correspond to: (a) a 200 aa residue DNRLRE domain; and (b) a 70 aa residue PEGA domain. We discuss the occurrence of these repeats and domains in the different proteins and genomes analysed in this work. Copyright © 2004 John Wiley & Sons, Ltd.