The coding region of the gene for the human beta 2-adrenergic receptor gene was fused to the beta-galactosidase gene of the lambda gt11 expression vector. The Y1089 Escherichia coli strain was lysogenized with this modified vector and transcription of the fusion gene was induced. Expression of this transcription unit was shown by the appearance in the bacteria of proteins of molecular weight higher than that of native beta-galactosidase, which are immunoreactive with anti-beta-galactosidase antibodies. Production of beta 2-adrenergic receptors was shown by the presence, on intact bacteria, of binding sites for catecholamine agonists and antagonists possessing a typical beta 2-adrenergic pharmacological profile. Binding and photoaffinity labeling studies performed on intact E. coli and its membrane fractions showed that these binding sites are located in the inner membrane of the bacteria. Expression of pharmacologically active human beta 2-adrenergic receptors in E. coli further supports the similar transmembrane organization proposed for bacteriorhodopsin and eukaryotic membrane-embedded receptors coupled to guanine nucleotide-binding regulatory proteins. Moreover, this system should facilitate future analyses of the ligand-binding properties within this family of membrane receptors.