TXW-1, aBorreliastrain isolated in March 1998 from an adult maleDermacentor variabilistick feeding on a coyote from Webb county, Texas, USA, was characterized by using randomly amplified polymorphic DNA (RAPD) analysis, RFLP and sequence analysis offlaBandrrs(16S rRNA gene), DNA–DNA hybridization analysis, SDS-PAGE and Western blotting with mAbs. It shows different banding patterns in RFLP analysis offlaBand forms distinct branches in phylogenetic analysis derived fromflaBandrrsgenes. It differs from other borreliae based on the banding patterns obtained by RAPD analysis. This strain contains a small, 38-kDa endoflagellar protein. DNA–DNA hybridization experiments revealed that the levels of DNA reassociation between TXW-1 and previously described relapsing fever borreliae were 38·64 % (Borrelia turicatae), 38·40 % (Borrelia parkeri), 7·39 % (Borrelia hermsii) and 18·30 % (Borrelia coriaceae). However, the level of DNA relatedness betweenB. parkeriandB. turicataewas 78·78 %. Sequence analyses offlaBandrrsgenes indicate that the similarities of nucleotide sequences among TXW-1 andB. turicataeorB. parkeriare less than that betweenB. turicataeandB. parkeri, and that the genetic distances among TXW-1 andB. turicataeorB. parkeriare greater than that betweenB. turicataeandB. parkeri. TXW-1 lacks anospCgene. Electron microscope observations showed that this spirochaete had different morphological structures compared to previously described relapsing fever borreliae. All the results obtained from the above-mentioned analyses indicate that TXW-1 is different from other describedBorreliaspecies and that it represents a novel species ofBorrelia. We have been unable to revive frozen cultures and so can not meet the requirements of the Bacteriological Code to deposit viable type material at two different culture collections. Therefore we use theCandidatusdesignation; based on these results, the species ‘CandidatusBorrelia texasensis' is proposed.