Section headings and selected papers: General Introduction. The role of gene transfer in bacterial evolution, J. P. W. Young. Evidence for Gene Transfer between Bacteria in Nature. Antibiotic resistance gene transfer in the environment: an overview, J. D. van Elsas. Methods for Studying Genetic Interactions in Terrestrial Environments. Detection of genetic exchange in the terrestrial environment, N. Cresswell & E. M. H. Wellington. Methods for studying conjugative plasmid transfer in soil, E. Smit & J. D. van Elsas. Methods for Studying Genetic Interactions in Aquatic Environments. The development of detection systems for pseudomonads released into lake water, C. Winstanley et al. Survival of genetically engineered microorganisms in activated sludge, J. C. Fry et al. Evaluation of Some Methods for Detecting Genes and Gene Transfer in Nature. The estimation of gene transfer in natural environments, J. R. Saunders & V. A. Saunders. Gene Transfer Between Fungi. Regulatory Aspects. Epilogue. Index.