Salivary, gingival crevicular fluid and serum-specific immunoglobulin G (IgG)-subclass antibodies to Actinobacillus actinomycetemcomitans leukotoxin were quantified by enzyme-linked immunosorbent assay. Samples were taken from six patients with periodontal pockets ≥5 mm, harboring A. actinomycetemcomitans in subgingival plaque and from six healthy, sex- and age-matched controls, who did not harbor A. actinomycetemcomitans. In individuals suffering from periodontitis, the median values of specific IgG1- and IgG2-subclass antibodies in saliva, gingival crevicular fluid and serum were, respectively IgG1 147 ng/ml, 5226 ng/ml and 7318 ng/ml and IgG2 4.8 ng/ml, 934 ng/ml and 860 ng/ml. In the patients, specific IgG3 antibodies were detected in one out of six individuals in saliva, in two individuals in gingival crevicular fluid and in five out of six patients in serum with a median value of 561 ng/ml. The median values of specific IgG4 antibodies in saliva, gingival crevicular fluid and serum were below detectable levels. The median values of the total IgG subclasses in saliva and serum were 14622 ng/ml and 10.3 g/l respectively. Individuals with periodontitis had, compared with controls, a higher ratio of specific IgG1 antibodies to total IgG1 in saliva (P<0.05) and in serum (P<0.05) and a higher ratio of specific IgG antibodies to total IgG in saliva (P<0.05) and in serum (P<0.01). The results show an elevation of both oral and systemic specific antibodies to A. actinomycetemcomitans leukotoxin.