cDNA clones encoding the BALB/c murine erythrocyte band 7 integral membrane protein (also termed protein 7.2b, or 'stomatin') were isolated by the screening of a corresponding bone-marrow lambda gt11 cDNA library with a human cDNA probe, and by 5'-RACE PCR cloning. Comparison of the murine, human and Caenorhabditis elegans protein 7.2b amino acid (aa) sequences revealed overall identities of 88% (human) and 61% (C. elegans), with the N-terminal domains showing only little similarity. The 7.2b protein sequences of the two mouse strains, BALB/c and C57BL/6J (B6), showed six rather conservative aa substitutions, three of them in the hydrophobic domain. The BALB/c murine mRNA, about 3.5 kb in size, is widely expressed in various tissues, most notably in spleen, lung and testis.