The aim of the present study was to examine the microbiota on the internal surface of the components of 28 Brånemark implants in 10 partially edentulous patients who had been treated with 1 fixed partial prostheses each. The prostheses had been in function for 1 to 8 years. The fixed prostheses were checked for mobility and removed. The abutment screws were loosened and classified as stable, easily removed or loose. Then, bacterial samples were obtained from the various internal surfaces of the implant system. Estimation and identification of the most predominant species was performed on the blood agar plates. Identification was based on Gram reaction, oxygen sensitivity and biochemical tests. Internal surfaces of different components of the Brånemark implants, after varying periods of function in the oral cavity, consistently harboured a heterogeneous and primarily anaerobic microbiota. The individual samples showed a great variation. No relation could be seen between type and length of abutment, abutment stability, bone loss and type and number of microorganisms found in the samples. The flora consisted mainly of facultative and anaerobic streptococci, Gram-positive anaerobic rods such as Propionibacterium, Eubacterium and Actinomyces species and Gram-negative anaerobic rods including Fusobacterium, Prevotella and Porphyromonas species. There are reasons to suggest that this presence of bacteria is the result of (i) a contamination of the fixture and abutment components during the 1st and/or 2nd stage of implant installation and/or (ii) a transmission of microorganisms from the oral environment during function subsequent to bridge installation.