Eikenella corrodens 1073, which has been shown to induce periodontal disease in experimental animals, was found to aggregate when mixed with human submandibular‐sublingual (SM‐SL) saliva. The purpose of this study was to isolate, purify and chemically characterize the substance that agglutinates E. corrodens cells (E. corrodens aggregating factor [Ec‐AF]). Ec‐AF was detected in SM‐SL saliva of all the donors tested, whereas E. corrodens aggregating activity was not detected in parotid saliva. Ec‐AF was purified from SM‐SL saliva by ECTEQLA‐cellulose column chromatography, ultrafiltration and gel filtration high performance liquid chromatography. An 81‐fold increase in the specific activity of purified Ec‐AF was achieved with a yield of 16.7%. Polyacrylamide gel electrophoresis of Ec‐AF in sodium dodecy) sulfate and β‐mercaptoethanol produced a single protein band corresponding to a subunit molecular weight of 140 000. Treatment of an identical gel with periodic acid‐Schiff reagent resulted in staining only of material coinciding with the Coomassie blue‐staining band, indicating that the Ec‐AF was a glycoprotein. Chemical analysis indicated that Ec‐AF is composed of protein (27.3%), neutral sugars (30.3%), hexosamines (24.9%), and sialic acid (17.3%). The polypeptide backbones of Ec‐AF contained 33% serine plus threonine and 36% proline plus alanine. The carbohydrate moety of Ec‐AF consisted of N‐acetylgalactosamine, galactose, fucose, sialic acid, N‐acetylglucosamine, with their molar ratio being approximately 2:2:1:1:1, respectively.