Experiments were designed to characterize a number of oral "pigmented"Bacteroidesisolates with regard to their pathogenicity in an experimental model system and a number of other properties. These include fatty acid determination, hemagglutination studies, collagenase and protease activities, and vitamin K. dependency. OralB.asaccharolyticusandB.melaninogenicusisolates differed from one another in phenylacetic acid production, hemagglutination, collagenase activity, and pathogenicity. AllB.asaccharolyticuswere found to be pathogenic in thein vivomixed infection model and this property could be correlated with biochemical and enzymatic activities.