The present study was performed to evaluate the clinical, microbiological and immunological aspects in the early stages of recurrent periodontal disease. After clinical monitoring of pockets with recent evidence of disease recurrence, microbiological samples for cultural analysis, serum and gingival crevicular fluid (GCF) samples were taken for IgG antibody analysis from 14 sites, 7 in 6 recurrent periodontitis patients and 7 in 7 periodontally healthy control subjects. IgG responses of serum antibody to 8 gram-negative bacterial strains were compared with those of GCF sampled from the recurrent site. The results clearly demonstrated the predominance of Bacteroides gingivalis in most subgingival plaque samples during the early stages of disease recurrence; the mean proportions of B. gingivalis were significantly different from those of the healthy sites (p less than 0.05). 4 out of 6 serum samples showed the elevated antibody responses to B. gingivalis 381; and this was closely correlated to homologous infection by this micro-organism in recurrent sites. Elevated serum antibody responses were also noted to Eikenella corrodens 1073 and Actinobacillus actinomycetemcomitans Y4. However, no relationship with homologous infection was found for A. actinomycetemcomitans. 3 out of 6 GCF samples had greater antibody titers than the serum, suggesting local antibody synthesis by the gingival cells in the recurrent pockets. The present study showed that B. gingivalis might play an important role in the pathogenesis of disease recurrence in its early stages.