Relative density (activity) of the tick Ixodes ricinus was determined in five districts of the Lublin region (eastern Poland) by vegetation flagging. Tick activity values were compared to the determined by ELISA tests seroprevalence to tick-borne encephalitis virus (TBEV) and Borrelia burgdorferi in forestry workers and farmers from the same areas. A significant correlation between tick activity and seroprevalence to both TBEV and B. burgdorferi antigen was found in farmers and in the total examined population.