The growth regulator 2, 3, 5 triiodobenzoic add (TIBA) was applied foliarly at the beginning of flowering (R1 stage) to a vining dry bean (Phaseolus vulgaris L.) genotype, grown symbiotically in a low nitrogen containing soil. Profiles of root nodule nitrogenase and leaf nitrate reductase activities, as well as of leaf chlorophyll content throughout the postflowering period, indicate that TIBA reduced the duration of nitrogen incorporation and caused early senescence. An increase in the number of pods per plant as well as in dry matter harvest index, supports the theory that TIBA causes bean plants to shift from vegetative to reproductive growth. No seed yield increase occurred as a result of TIBA application. Symbiotic nitrogen fixation alone may not provide sufficient nitrogen to allow optimal development of an increased number of pods. Further trials under higher soil nitrogen levels are suggested.