The aim of the paper was an attempt to correlate clinical signs with the presence of DNA of Borrelia burgdorferi (sensu lato) s.l. and the antibodies against B. burgdorferi s.l. in the blood of dogs. Among the animals studied there were 62 dogs delivered to the Veterinary Clinic in Szczecin and 30 from the Municipal Animal Shelter in Szczecin with varied clinical signs of borreliosis. In all cases the owners admitted frequent contacts of their dogs with ticks, both in the past, as well as shortly before the onset of sickness. We used two methods: PCR for detecting DNA of B. burgdorferi s.l. and ELISA test for detecting antibodies against the spirochete. Lameness, the principal symptom of canine borreliosis was the most frequent symptom of the group of 31 PCR-positive animals. The other most common symptoms in PCR-positive dogs were fever, swelling of joints and loss of body weight. DNA of B. burgdorferi s.l. was most frequently detected in the blood of dogs of the group 2-5 years old (13/54.1%). ELISA tests specific for IgG antibodies were positive in 37 of 92 sera (40.2%) taken from examined dogs. Lameness was observed in 15 of 37 IgG-seropositive dogs and in 25 of 55 seronegative animals. In 54% of dogs with the antibodies, swelling of instep- and wrist joints was observed compared to only 24.4% in seronegative dogs. An attempt to correlate the PCR results with the results of tests detecting antibodies against B. burgdorferi s.l. revealed that fewer than half (45.1%) of the dogs with presence of DNA of the spirochete, developed an immune response. Therefore the transfer of B. burgdorferi s.l. form, the primary lesion to the target tissues, is possible in dogs which did not develop immune response or develop an insufficient response. Among 92 borreliosis-suspected dogs 54 (over 58%) were diagnosed positively using laboratory methods. In most cases there was a correlation between clinical symptoms of borreliosis and presence of DNA B. burgdorferi, thus PCR may contribute to improving to a large extent diagnostic of canine Lyme disease.