To determine if dogs could serve as a reservoir for Borrelia burgdorferi, three beagles were inoculated subcutaneously (SQ) with 200 laboratory cultured spirochetes which were originally isolated from blood of a Peromyscus leucopus from Ft. McCoy, Wisc. One four month old beagle was inoculated SQ with 5 ground Ixodes dammini from Shelter Island, N.Y. which came from an area with a 50% B. burgdorferi tick infection rate; and another uninfected four month old beagle was housed loose on the floor with the tick inoculated dog. All three spirochete inoculated beagles developed IFA antibody titers to B. burgdorferi of (7 log2) to (8 log2) by day 28 post inoculation. All were apparently healthy and no spirochetes were cultured from the blood. In an attempt to exacerbate the disease two of the dogs were given 3 mg of dexamethasone on day 68 post inoculation. B. burgdorferi was isolated from blood of all these dogs on days 4 and 97 days post inoculation. The tick inoculated dog developed a B. burgdorferi IFA antibody titer of (10 log2) by day 14 post inoculation. The contact exposed dog also developed a B. burgdorferi IFA antibody titer of (7 log2) on post contact day 21 indicating contact infection. B. burgdorferi was not isolated from either of these dogs. These results indicate that, contact transmission of B. burgdorferi may occur between dogs, dogs can be subclinically infected with B. burgdorferi and have persistent infections.