This thesis reports on investigations carried out to identify the important antigens inducing a humoral immune response in periodontal disease. A number of different techniques were used. The first study examined the systemic immune response, specifically the effects of treatment on the immune response of patients with chronic periodontitis against a panel of periodontal pathogens and a large panel of antigen preparations from these bacteria. The results of the study indicated that there was no difference in antibody titre following treatment against any of the putative periodontal antigenic targets tested. These results conflict with many published reports, however, differences in factors such as length of treatment and antigen preparation often make the comparison of different studies futile. An investigation to examine the phenomenon of cross-reactivity between antibodies induced against putative periodontal pathogens was the second part of this overall project. The results suggested a high proportion of cross-reactivity between the 4 periodontal pathogens P. gingivalis, A. actinomycetemcomitans, P. intermedia and B. forsythus. Results indicating such a high cross-reactivity between these micro-organisms prove that the issue of cross-reactivity is an important one that should be considered when carrying out any immunological and microbiological investigations in this field. Following the above investigations of the systemic immune response the remainder of this thesis is a report of three studies examining the local immune response in periodontal disease.