The capacity of five common bean genotypes from the germ plasm bank at CIAT, Colombia (Río Tibaji, APN 18, Carioca, G 14665, and G19441) to fix nitrogen from the atmosphere was evaluated. An experiment was carried out with plants grown in 16-liter capacity plastic boxes with a highly aerated and nitrogen-free nutrient solution (400 ml of air/solution liter/min). In the first box the CIAT 899 Rhizobium strain was innoculated, and in another box the CR 477 strain from Costa Rica, both from CIAT; a third box was reserved for CF1 of national origino The experimental design consisted of random blocks with four repetitions. In order to determine the dry mass of the aereal part (DMAP), the radicular dry mass (RDM), and the nodular dry mass (NDM), the plants were cut in the R7 developmental phase. With respect to NDM, the carioca genotype and the CF1 strains were statistically superior to the rest (P<0,00l); however, the major nitrogen fixers were the G 14665 genotype - the best combination between NDM and fixation efficiency - and the CIAT 899 strain, which was 2.4 times more efficient (N mgl NDM g) than the rest. This shows that the NDM production is not a determining variable when genotypes or strains with a high capacity for nitrogen fixation in the atmosphere are being selected.