Since the beginning of the decade, when HOLSTEN and co-workers (1971) succeeded in establishing the symbiosis between soybean root cells and Rhizobium japonicum ?in vitro?, other research workers have been trying to repeat the experiment. The objective of the present work was to test the methodology applied to establish the symbiotic relationship between bean root cells and R. phaseoli Specific techniques of tissue culture were used to obtain callus in bean plants with subsequent inoculation with promising R. phaseoli strains, such as 127-K17 and 3610, in two culture media. Correlated studies were also made to evaluate the ability of different strains of R. phaseoli to fix dinitrogen in culture medium in the absence of plant cells. The method used in the studies of Rhizobium x bean tissue culture, consisted of obtaining and growing calli and inoculating them with a pure culture of Rhizobium bacteria. The morphology of the inoculated cells was observed by light microscope for the four experiments. Five experiments were conducted to check the ability of fifteen strains of R. phaseoli to fix atmospheric dinitrogen asymbiotically. Nitrogenase activity (enzyme responsible for biological nitrogen fixation) was evaluated using the acetylene reduction technique and gas chromatography for all experiments. The results of the ?in vitro? experiments were not reproducible, which suggests that the techniques used should be improved. Only two R. phaseoli strains fixed dinitrogen asymbiotically reproducibly (3610 and C-13). The others were not reliable as the results were not reproducible. It was concluded that free dinitrogen fixation by R. phaseoli depends on two factors: low levels of mineral nitrogen and tricarboxylic acid cycle intermediates in the culture media and microaerophilic conditions to enable expression of nitrogenase activity, as found with other Rhizobia already studied.