Few investigations on the development of dental have considered the first changes which can occur on a cleaned tooth surface during the first 4 h of exposure to the Plaque oral environment. The present study has investigated, using the scanning electron microscope, the colonization of enamel surfaces in vivo, and some of the factors influencing plaque formation during the initial 24 h after cleaning. A correlation was established between gingival health and the time of deposition of the organisms, and this fact, together with the presence of bacterial aggregates adjacent to the gingiva, is taken as an indication that the gingival fluid plays an important part in the colonization of the tooth surface. It is concluded that the formation of microbial plaque is an extremely complex and dynamic process encompassing a number of interrelated factors. It is suggested that two major processes are involved, firstly the adherence of bacterial aggregates and secondly growth of organisms within the aggregates and from residual material in enamel defects. The development of the plaque is considerably influenced by the local environment.