A sedimentation method for studying adsorption of microorganisms onto hydroxyapatite is described and compared with batch adsorption experiments. Data, which demonstrate the feasibility and the high reproducibility of the method, are reported for oral microorganisms collected from one individual and for one laboratory strain, KPSK 2, of Streptococcus mutans. It is concluded that the sedimentation method in combination with results from the batch experiments will give significant information on mechanisms involved in bacterial colonization of the tooth surface.