This study investigates the transfer of R factors, specifically those of the compatibility class P, between *Escherichia coli* K12 and *Rhizobium leguminosarum*. The R factors were stable in *R. leguminosarum* and conferred similar levels of antibiotic resistance, except for carbenicillin resistance, which was significantly reduced. Transfer between *R. leguminosarum* strains was facilitated by conditions favoring spheroplast formation, and no evidence of R factor-mediated recombination was observed. The study also explored the effects of medium composition, particularly the addition of nutrients like sodium nitroprusside (NB) and glycine, on R factor transfer. High levels of these nutrients inhibited bacterial growth and reduced the frequency of transfer. Additionally, the wide range of *R. leguminosarum* strains capable of receiving R factors and the inability to demonstrate chromosomal marker transfer through R factor-mediated recombination were noted. The results confirm that *R. leguminosarum* can act as a recipient or donor of P group R factors, providing a method for demonstrating conjugation in this species.This study investigates the transfer of R factors, specifically those of the compatibility class P, between *Escherichia coli* K12 and *Rhizobium leguminosarum*. The R factors were stable in *R. leguminosarum* and conferred similar levels of antibiotic resistance, except for carbenicillin resistance, which was significantly reduced. Transfer between *R. leguminosarum* strains was facilitated by conditions favoring spheroplast formation, and no evidence of R factor-mediated recombination was observed. The study also explored the effects of medium composition, particularly the addition of nutrients like sodium nitroprusside (NB) and glycine, on R factor transfer. High levels of these nutrients inhibited bacterial growth and reduced the frequency of transfer. Additionally, the wide range of *R. leguminosarum* strains capable of receiving R factors and the inability to demonstrate chromosomal marker transfer through R factor-mediated recombination were noted. The results confirm that *R. leguminosarum* can act as a recipient or donor of P group R factors, providing a method for demonstrating conjugation in this species.