Extra Parotid Glycoprotein (EP-GP) is a glycoprotein isolated from human saliva, having homologues in several other body fluids. The biological role of EP-GP and its homologues is unknown. Recently, EP-GP was shown to bind in vitro to the bacterium Streptococcus salivarius HB. In contrast, no binding to a number of other oral microorganisms could be demonstrated. In the present study we have determined whether binding of EP-GP to bacteria occurs in vivo in saliva and in other EP-GP containing body fluids. Therefore the presence of EP-GP on bacteria in vivo was determined by analyzing oral, skin and ear floras by confocal fluoresence microscopy using specific antibodies. About 12% of the in vivo oral flora had EP-GP present on their surface, while approximately 5% of the bacteria from ear canal or skin was positive for EP-GP. IgA was detected on approximately 65% of the salivary bacteria, whereas the high-molecular weight mucin (MG1) and cystatin C were not detectable on any oral bacterium. Using a replica-plate assay, a number of EP-GP binding strains in saliva were isolated and identified as Gemella haemolysans, Gemella morbillorium, Streptococcus acidominimus, Streptococcus oralis, Streptococcus salivarius and Streptococcus parasanguis. Bacteria from the ear canal and skin bacteria were identified as Staphylococcus hominis. It is concluded that EP-GP is selectively bound in vivo to several oral and non-oral bacterial species.