Sera of 500 inhabitants of north-eastern Poland, 450 suspected for Lymeborreliosis and 50 blood donors (control group), were analysed for the presence of IgG antibodies againstAnaplasma phagocytophilum, the causative agent of human anaplasmosis (HA), known so far as human granulocyticehrlichiosis (HGE). Forty one (9.1 %) sera of the study group and one serum (2 %) of the control groupwere positive using indirect fluorescence assay (IFA). The seropositivity tended to be more frequentamong males (10.3 %) than females (7.6 %) and among the rural (10.3 %) than urban population (7.5 %);however, differences were of no statistical significance (p = 0.4). No age difference was found betweenthe seropositive and the seronegative individuals (p = 0.77). The only factor increasing the risk ofHA seropositivity found was forestry employment (p < 0.05). Additionally, a total of 559 Ixodes ricinusticks, collected in the same area as sera, were investigated for the presence of A. phagocytophilum bythe polymerase chain reaction (PCR) and 41 (8.7 %) of them were found to be positive. The infection levelranged from 2.3-13.7 %, depending on the area studied. Bacteria were significantly less frequently detectedin nymphs - 2.1 % (5/235) than in adult ticks - 13.6 % (44/324) and in males--4.2 % (74/165) than infemales--23.3 % (37/159) (p < or = 0.05). The obtained results confirm both the occurrence of HA fociin north-eastern Poland with I. ricinus as the principal vector of the A. phagocytophilum infection,and forestry workers as the main group at risk.