Plant growth and root nodules of infected Faba bean plants with broad bean mottle virus were significantly reduced in plant height, leaf area, dry matter, number and size of nodules in comparison with healthy ones. As well Leghaemoglobin content and Nitrogenase activity were reduced in infected nodules at 45 days after BBMV inoculation. The amount of N₂-fixed as expressed by acetylene reduction was reduced considerably by 38.8%. Nitrogen content as an indicator for the efficiency of N₂-fixation was reduced in shoots, roots and root nodules of infected nodulated plants as compared with healthy nodulated ones. Differences between bacteroids in healthy and in BBMV infected cells were no longer apparent. These differences include: (i) a decrease in endocytotic and exocytotic vesiculation on the membrane envelope of the bacteriods and on plasma membrane of bacteroidal cells, (ii) a decrease in number of vesicles in the space between the bacteriod and the membrane envelope. The possible significance of these changes relative to the decreased efficiency of N₂-fixation was discussed.