The paper deals with the intensity of local and systemic immune response to the antigen stimulation of dental plaque in experimental gingivitis. Three groups, each of 11 rats, were in contact with S. mutans, F. nucleatum, A. viscosus and B. gingivalis in order to stimulate gingival inflammation. Experimental days were 0, 3rd, 7th and 14th day. Before sacrificing experimental animals condition of gingival tissue was assessed. Gingival specimens were then taken for numeric density analysis as well as serum for antibody titer measurement. None of the young rats developed gingivitis during the experiment, whereas the adult immunized rats bled on probing. The greatest increase of the number of lymphocytes occurred in the elder immunized group and the lowest in the group of one month old rats. Serum antibody titers were low in young rats, moderate in adult and high in adult immunized rats. These results indicate that adult rats reacted stronger to plaque antigens than young rats and that previous contact with the antigens increased the reaction.