Relapsing fever is a worldwide, endemic disease caused by several spirochetal species belonging to the genus Borrelia. Oms38 (outer membrane-spanning protein of 38 kDa) is present in the outer membranes of B. duttonii, B. hermsii, B. recurrentis and B. turicatae as well. Characterization of Oms38 was performed using the black lipid bilayer method, which demonstrated that Oms38 forms small, water-filled channels of 80 pS in 1 M KCl that did not exhibit voltage-dependent closure. The Oms38 channel is slightly selective for anions and shows a ratio of permeability for cations over anions of 0.41 in KCl. Analysis of the deduced amino acid sequences revealed that Oms38 contains an N-terminal signal sequence which is processed under in vivo conditions. Oms38 is highly conserved within the four studied relapsing fever species, sharing an overall amino acid identity of 58% and with a strong indication for the presence of a ß-barrel formation. DipA (BB_0418) forms a porin specific for dicarboxylates which may play an important role for the uptake of specific nutrients in different Borrelia species.