A NATO ASI on "Molecular Ecology of Aquatic Microbes" was held at II Ciocco, Lucca, Italy from 28 August - 9 September 1994. The aims of the ASI were to evaluate the potential for molecular biology to solve some important questions in aquatic microbiology, particularly in relation to biogeochemical cycling and microbial physiology. Techniques developed by molecular biologists have now been adopted by a wide range of scientific disciplines. In the last 5 years, aquatic microbial ecologists have begun to incorporate these methods into their research and, as a result, are developing a much clearer understanding of phylogenetic diversity, the molecular basis of physiological acclimations and the transduction of environmental