Lack of suitable gene transfer techniques hampers genetic improvement and analysis of several industrially and clinically important gram-positive bacteria. Techniques already developed are often difficult to reproduce and limited in application. This study examines the feasibility of expanding the techniques available through the use of conjugation as a broad host range gene transfer mechanism. Such systems have been developed for gram-negative bacteria. Theoretical and practical aspects, important for development of such a system for gram-positive bacteria were examined, Transformation of various gram-positive bacteria with the broad host range plasmid pAM£l, and other vector plasmids of grampositive origin was attempted. Conjugation of pAH)31 from S. la c tls to a range of gram-positive bacteria was carried out. The relationship between pAMJ31 and other plasmids was examined on the basis of DNA homology. The stability of pAXJ31 in various recipient strains was also examined. Finally, conjugation between gram negative and positive bacteria is reported for a shuttle plasmid harbouring the mob site of RP4. The presence of the mob site allows mobilization of this plasmid to streptococcal species in matings with an E.coll strain which has the RP4 transfer functions chromosomally integrated.