Porphyromonas gingivalis(P. gingivalis) has been isolated frequently and in high numbers from periodontal pockets of adult patients with advanced periodontitis, while the organism is recovered rarely and only in low numbers from healthy gingival sites1-3). Many virulence determinants of P. gingivalis are cell surface components or extracellular products, such as capsules, toxins, and enzymes, and their synthesis and secretion can be markedly affected by growth conditions3). In the host, the growth of pathogens is at submaximal rates when the essential nutrients or cofactors are at growth-limiting concentrations. Indeed, it has been argued that some virulence determinants might only be expressed in vivo, due to specific growth conditions, while potential factors identified in the laboratory may play little or no role in disease4). For studying virulence factors of pathogens in the laboratory, it is important to take into account the growth conditions that exists in the host. Even though the precise environmental conditions at any one time in a periodontal pocket or in an animal model during the course of an infection are not known, it has been shown recently that growth of a number of pathogenic Gram-negative bacteria either in chambers implanted in animals or at sites of infection in humans is either iron limited or severely restricted by the availability of iron. Thus, the ability to compete for iron with the host will contribute significantly to the virulence of an organism3), 5-6). The black-pigmented Bacteroides spp. which includes P. gingivalis cannot utilize free iron, but they do have a requirement for heme. It is signigicant that P. gingivalis has been found to be most effective at degrading the iron-transporting plasma proteins albumin, 대한치주과학회지 : Vol. 27, No. 3, 1997