Oral strains of Fusobacterium nucleatum showed haemagglutination (HA) of sheep red blood cells and attachment of HA-active F. nucleatum fragments to other microorganisms allowed a means of studying microbial surface interactions. HA-active sonicated fragments (SF) prepared from F VSports手机版. nucleatum were mixed with whole cell suspensions of 48 bacterial strains and, after incubation, the whole cells were separated from the non-absorbed fragments by differential centrifugation. Attachment of F. nucleatum fragments to the cells was indicated by a reduction in the HA activity of the SF in the supernatant fluid remaining after absorption with whole cells. HA activity of the microbial cells used for absorption and the detection of F. nucleatum fragments on these cells by an indirect fluorescent antibody technique provided further evidence of attachment. Of the 48 strains tested, 10 absorbed F. nucleatum HA-active fragments. They included Bacteroides gingivalis, Bacteroides fragilis subsp. distasonis, Bacteroides corrodens, Streptococcus morbillorum, Streptococcus sanguis (Blackburn and JC 74) and Streptococcus mutans AHT, BHT, 10449 and 6715. Chelators revealed that F. nucleatum attached to the microorganisms via a Ca2+-dependent interaction. Sugar inhibition demonstrated that F. nucleatum attached to the microorganisms via a D-galactose-containing moiety on their surface. A reduction in the absorption of F. nucleatum HA-active fragments by Strep. mutans grown in a higher concentration of sucrose was observed. .