The adherence of bacteria to implanted medical devices is believed to be important in the development of implant associated infections. Measures which reduce bacterial adherence should reduce the incidence of these infections. However, in order to assess the importance of adherence, the effectiveness of methods to reduce adherence, and compare data from different laboratories, the conditions of the in vitro studies on adherence need to be specified. There are currently no correct and incorrect methods, however, methods used need to be carefully described. The studies reported here indicate that the definition of adherence needs to be established, with the use of polystyrene as the reference material recommended. Since the adherent organisms lose adherence traits with culture, cultures must be selected for adherence regularly. It is important to control the number of organisms/ml but the volume used is not important. The medium used to grow the organisms and the use of stationary, rocking or flow conditions will alter adherence and need to be specified and be consistent within a set of experiments. Culture conditions, methods of rinsing the material, methods of elution and counting, or direct counting of organisms on the material need to be specified. Finally, as much information as possible on the bulk and surface properties of the material should be provided. The handling of the material for the experiments should be careful and defined. Fingerprints, contact with protein, wet surfaces vs dry surfaces, etc., will all affect the subsequent adherence. The materials should not be re-used since the removal of the adherent proteins or the biofilm is very difficult. Progress can be made in this important area if the details of procedures are specified.