The B806-866 antenna complex was isolated from cytoplasmic membranes of the green thermophilic bacterium Chloroflexus aurantiacus. The membranes were treated with 7 M urea at 50 degrees C, the B806-866 antenna complex was solubilized with a mixture of Noni-fjdet P-40 (octylphenoxypolyethoxyethanol (Sigma)) and sodium dodecylsulphate (2:1) and isolated by sucrose density gradient centrifugation. This antenna complex was characterized by reversed-phase chromatography (fast polypeptide and polynucleotide liquid chromatography), amino acid and sequence analyses. The B806-866 antenna of Chloroflexus aurantiacus consists of two polypeptides: the B806-866-alpha and B806-866-beta polypeptides in an apparent stoichiometric ratio of 1:1, which may be equivalent to the structural elementary unit found in the antenna systems of many species of Rhodospirillaceae.