With the objective of evaluating, in the field, the antagonism of Rhizobium leguminosarum biovar phaseoli against Rhizoctonia solani, two experiments were established in the zones of Santa Rosa de Pocosol (Alajuela) and Sabanilla de Montes de Oca (San José), in two different sowing seasons. The stocks CR- 455, CR-477, CR-487, CR-422 and CIAT-632, were evaluated and were inoculated with R. solani. Besides the stocks we included the following treatments: Absolute Witness (AW), with no R. solani inoculation, with no nitrogen added(-N, -R); +N-R (+140 kg N/ha, with no R. solani inoculation); +N+R (+140 kg N&ha, with R. solani inoculated). The soil was inoculated utilizing rice husks colonized by R. solani, at a dosis of 14,5 g/m2.. We evaluated the variables: porcent of germination, plants height and infection rate. We performed the evaluations at 8 and 18 days after germination. We utilized the design of complete blocks ramdomly located with six repetitions per treatment. The variable of plant height did not show any differences between treatments in any of the zones. The treatment with fungicides was the one which showed more germination percentages in both experiments. In Pocosol, all the stocks sho wed some inhibition effect towards the fungus (P<0.05), but only during the period of the first evaluation. In Montes de Oca, we observed a larger inhibiton effect thant the one in Santa Rosa; the stocks CR-487 and CR- 422 showed smaller I.I than the witness in the first evaluation (P<0,05), and they all showd significant differences on what concerns the +N+R treatment for the same variable, during the second evaluation.