Provided here is an up-to-date survey of gene transfers in

the main natural habitats, with a special reference to

genetically engineered microorganisms.In the first of five

sections technical approaches of gene transfer in the

natural environment are developed. These emphasize the use

of modernmethodologies for the detection of recombinant

bacteria in natural waters and soil, using DNA or rRNA

probes and PCR technology. The three following sections deal

with various aspects of gene transfer in aquatic

environments, terrestrial habitats and human and animal gut.

These include transfer of plasmidic or chromosomal markers

through either conjugation, mobilization, transformation or

transduction processes. Also covered are factors influencing

survival of cells harbouring the transferred genes in these

environments. The last section is devoted to an examination

of scientific and ethical problems related to the release of

genetically engineered microorganisms.