Six new mutations conferring erythromycin - resistance in Bacillus subtilis have been isolated and genetically analysed by means of DNA-mediated transformation. It has been possible to order tentatively these mutations relative to one another. One of these mutants had the unusual property of yielding transformants when exposed to DNA extracted from itself. The authenticity and reproducibility of this phenomenon was first confirmed and it was then further studied. Although the mechanism by which this occurs has yet to be explained, the following conclusions have been reached: (1) the observed phenomenon is not associated with all ery mutations but only the one with which it was first associated (2) "selfing" is determined by a mutation distinct from the one conferring erythromycin resistance (3) in a recombination - deficient mutant, "selfing" is depressed to the same extent as normal transformation and therefore probably requires recombination events for expression. The different genotypes emerging from such transformation have been analysed and their origin speculated upon. Throughout this thesis, a distinction is made between those conclusions that are definite and those that are tentative and uncertain.