Infectious complications caused by genus Ehrlichia were confirmed when samples taken from patients with Lyme borreliosis with non-characteristic development and those sent directly by physician who treated the patient were examined. Laboratory diagnostics of ehrlichiosis was based on hematological examination of blood, on anamnestic and epidemiological data, on indirect immunofluorescence serology verified using Western blot test with specific antigen and by determination of DNA agents using polymerase chain reaction analysis (PCR). From 37 goal-directed examinations done in years 1998-2000, bacteria Ehrlichia chaffeensis was found to be the cause of human monocytic ehrlichiosis (HME) in two patients who had stayed in Bulgaria, USA and Thailand. DNA of E. chaffeensis was confirmed by PCR with subsequent product sequentiation (determination of the order of pairs of the oligonucleotide bases). In both patients monocytosis and positive antibodies in indirect immunofluorescence were found. The agent of human granulocytic ehrlichiosis (HGE) caused by group Ehrlichia phagocytophila was determined in three serologically positive patients using PCR and Western blot test with specific antigen P44. Cocobacils were identified electronmicroscopically in intracytoplasmatic vacuoles of isolated leukocytes. Coincidence of Borrelia afzelii and Ehrlichia sp. was found in the blood of a woman patient with erythema migrans formed in the place where from the tick's nymph was removed one week earlier. Cutaneous manifestations were accompanied by subfebrilia, myalgia and gastroenteritis. The patient was positive for both agents in Western blood and PCR. DNA of Borrelia and Ehrlichia was isolated from the patient's blood and urine in the first week of illness. Further study and an increase of sensitivity of the g. Borrelia and Ehrlichia cultivation become necessary to clarify the role of ehrlichias in the disease in our conditions.