The use of sheep as a suitable animal model of destructive forms of human periodontal disease has been assessed from comparative radiological, histological, and serological investigations of sheep with and without periodontal disease. The results showed that, in sheep with periodontitis, bone resorption, collagen breakdown, degradation of blood capillary vessel walls, cellular infiltration of plasma cells, lymphocytes, and epithelial infiltration were significantly greater than in sheep without periodontitis, and the features are similar to those in rapidly destructive forms of periodontal disease in man. The levels of serum IgG antibody reactive against B. gingivalis antigens (measured by ELISA) were significantly higher in sheep with periodontitis than those without, similar to the association reported in some types of human periodontal diseases. These findings suggest that periodontitis in sheep could represent a suitable animal experimental model for certain types of rapidly destructive human periodontal diseases.