LongoVital is a herbal tablet with documented immunostimulatory effects in man. In the present study the effect of LongoVital on development of periodontal disease was investigated in a rat model. Fifty‐four conventional rats, 5 wk old, were distributed into the following groups: A) untreated, uninfected; B) untreated, infected withActinomyces viscosusandPorphyromonas gingivaliswk 8; C) treated with LongoVital 80 mg × 3/wk, wk 5–14, uninfected; D) treated with LongoVital 80 mg × 3/wk, wk 5–14, infected withA. viscosusandP. gingivaliswk 8; E) treated with LongoVital 200 mg × 1 in wk 8 and 80 mg wk 9–14, uninfected; F) infected withA. viscosusandP. gingivaliswk 8, subsequently treated with LongoVital 200 mg × 1 in wk 8 and 80 mg wk 9–14. All animals were killed when they were 15 wk old, and periodontal bone support was assessed radiographically. Statistically significant bone loss was found in untreated, infected rats, as compared with untreated, uninfected rats. In LongoVital‐treated animals, no significant difference was seen in bone level between infected and uninfected rats. These results indicate that LongoVital‐treated rats were protected against periodontal bone loss caused by infection withA. viscosusandP. gingivalis. Furthermore, the protection seemed effective both when LongoVital was administered prophylactically and after exposure to periodontal pathogens. The active components of LongoVital, as well as the mechanisms responsible for the protectio