The determination of the nitrogen fixed from the air by bacteria in association with sword bean (Canavalia ensiformis D. C.) and cowpea (feijão baiano) (Vigna sinensis (L.) Savi) was the main purpose of this work. The two leguminous plants were sown in Mitscherlich pots filled with 6 kg of "terra-roxa-misturada" soil, collected at the depth of 20 cm in the Central Experiment Station, Instituto Agronômico, Campinas County. The following treatments with three replications were compared: 1) check; 2) NPK; 3) NPK + limestone; 4) NPK + inoculant; 5) NPK + limestone + inoculant; 6) PK + limestone; 7) PK + limestone + inoculant. The amount of limestone was calculated to raise the pH to 6.5 and the base saturation of the sail to 70%. The fertilizer applications for N, P2O5,. and K2O were 2.0 g, 2.2 g and 3.0 g respectively, as solutions of NH4NO3, K2HP0(4) and KCl. Harvesting was done at the beginning of blooming-time by cutting the plants even with the ground. Later, both the aerial parts, as well as the roots, were weighed fresh and after drying at 60° C. Nitrogen determination by the Kjeldahl method of these two fractions, aerial parts and roots, were mode after drying. The soil from those pots without nitrogen fertilizer were submitted to the same analysis for comparison with the initial level of this element in the soil. The data obtained indicate that the two leguminous plants showed a good nitrogen fixation capacity and that the feijão baiano was more effective. The amounts of nitrogen fixed in pots that received the best treatments corresponded to 48.5 kg per hectare for the sword bean and 73.0 kg for the "feijão baiano". From this point of view both leguminous plants were satisfactory to be employed as green manure.