The aim of study was evaluation of seasonal prevalence of antibodies against Borrelia burgdorferi in Białowieza area, that is Lyme borreliosis endemic region. IgM and IgG antibodies against 41-kDa antigen of Borrelia burgdorferi B31 strain were investigated with ELISA in sera of 300 Białowieza inhabitants between September 1993 and May 1994. Moreover in 40 asymptomatic persons, that were seropositive in September 1993, additional control was performed in May 1994. The highest prevalence of IgM antibodies was observed in September 1993 (43.4%), with decrease during winter and spring (down to 15.7% in April) and accompanying the highest prevalence of IgG antibodies (17.7%) in April 1994). From 33 persons, that revealed IgM antibodies in September 1993, 3 (9%) were still seropositive, 4 (12%) cleared IgM antibodies and became IgG-seropositive, and remained 26 (79%) had no antibodies. Specific IgG antibodies found in 7 persons in September, were still present in 4. Obtained results indicate necessity of taking into consideration seasonal dynamics, when results of seroconversion against Borrelia burgdorferi between different areas and different populations are compared.