Host immune response and the predominant subgingival microflora were evaluated in a 47-year-old male exhibiting severe, recurrent periodontitis. The patient's neutrophils were chemotactically elevated but other functions were within normal limits. Significantly, Bacteroides gingivalis and Bacteroides zoogleoformans constituted 80% of the cultivable microflora and total cell count in subgingival plaque. The remainder of the cultivable microbiota was comprised of Fusobacterium nucleatum and Haemophillis aprophillis. The present study provides additional evidence for an association between B. gingivalis and severe, recurrent periodontal disease.