ABSTRACT This study aimed to clarify how concentrations of vitamin C in plasma relate to the serology of periodontitis. The random sample used comprised 431 men, 194 from Finland and 237 from Russia. The plasma vitamin C concentration was determined by o -phtaldialdehyde-fluorometry, and serum immunoglobulin G antibodies to Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis were determined by a multiserotype enzyme-linked immunosorbent assay (ELISA). The mean plasma vitamin C concentration was higher ( P < 0.001) in Finnish subjects (mean ± standard deviation, 4.5 ± 2.8 mg/liter) than in Russian subjects (1.4 ± 1.8 mg/liter). Mean antibody levels to both A. actinomycetemcomitans (4.7 ± 3.6 versus 5.2 ± 3.1 ELISA units [ P = 0.05]) and P. gingivalis (5.7 ± 2.5 versus 7.6 ± 2.9 ELISA units [ P < 0.001]) were lower in Finnish men than in Russian men. In the combined Finnish and Russian population, the antibody levels to P. gingivalis were negatively correlated with vitamin C concentrations ( r = −0.22; P < 0.001); this association remained statistically significant ( P = 0.010) in a linear regression model after adjustment for confounding factors. The proportion of P. gingivalis -seropositive subjects decreased with increasing vitamin C concentrations ( P for trend, <0.01), but no trend was seen among A. actinomycetemcomitans -seropositive subjects. In conclusion, P. gingivalis infection is associated with low concentrations of vitamin C in plasma, which may increase colonization of P. gingivalis or disturb the healing of the infected periodontium.