Pheasants, Phasianus colchicus L., constitute a major part of the ground-feeding avifauna of England and Wales and are important hosts to immature stages of Ixodes ricinus L., the principal tick vector of Lyme borreliosis spirochetes in Europe. Therefore, their competence as hosts for Borrelia burgdorferi Johnson, Schmid, Steigerwalt & Brenner sensu lato was investigated. One group of pheasants was inoculated by needle with 1 x 10(6) cultured B. burgdorferi s.s. organisms, and a 2nd group of birds was infested with I. ricinus nymphs collected from a focus of Lyme borreliosis in southern England. Both bird groups were subjected to xenodiagnoses using uninfected I. ricinus nymphs. All recovered engorged ticks, as well as pheasant skin biopsies, were analyzed by a nested polymerase chain reaction targeting the 5S-23S rRNA genes of B. burgdorferi s.l. Both groups proved to be infective for ticks. The birds that were infected by tick bites proved to be significantly more infective for ticks (23% of the xenodiagnostic ticks positive) than those infected by needle (5%). The results show that pheasants can be infected experimentally with B. burgdorferi s.l., that they can pass the spirochetes to ticks and that their infectivity for ticks may persist as long as 3 mo. We conclude that pheasants are reservoir competent for Lyme borreliosis spirochetes and potentially play an important role in the maintenance of B. burgdorferi s.l. in England and Wales.