The aim of the study was to determine the correlation between serum C-reactive protein (CRP) levels, the presence of antibodies to B. burgdorferi, and the occurrence of clinical signs of Lyme borreliosis in Bernese Mountain Dogs (BMDs). The study included 54 BMDs divided into three groups. The first group (n = 29) consisted of animals with signs suggestive of Lyme disease and rapid tests showing the presence of antibodies to B. burgdorferi in their serum. The second group (n = 15) included dogs that did not show signs of Lyme disease and had antibodies to spirochetes in their serum. The third group consisted of BMDs (n = 10) that showed no signs of disease and in whose serum no antibodies to B. burgdorferi were detected by rapid tests. Of the 29 dogs in the first group, 18 had elevated CRP levels. These animals showed signs of arthritis and renal failure. After treatment with doxycycline, the clinical signs of the disease disappeared, and the CRP concentration decreased to normal levels in 16 dogs. In the second group, 2 animals had elevated CRP levels, while in the third group, no antibodies to spirochetes were detected in the serum of any of the dogs, and CRP levels remained within the physiologically normal range. Our own observations indicate that C-reactive protein is a promising marker for monitoring the effectiveness of Lyme disease therapy in BMDs, as well as for distinguishing asymptomatic positive seroreagents from dogs of this breed that are actually suffering from the disease. However, to confirm its usefulness, further research is needed on representatives of this breed, especially those suffering from a chronic form of the disease.