Many cross-sectional and longitudinal clinical studies have established that advanced caries lesions are associated with a higher prevalence in dental plaque of mutans streptococci4 and lactobacilli. However, such studies are generally made on fissures or approximal enamel surfaces of teeth still in position in the mouth. Caries diagnosis of such sites has to rely on relatively insensitive techniques such as radiographs or tactile criteria; by the time a lesion can be reliably diagnosed in this way it is relatively well advanced. It is possible that the bacteria associated with the established lesion may not be the same as those responsible for its initiation. The aim of this short review is to consider whether there is any evidence that bacterial succession occurs during demineralisation of the enamel surface.