Investigations were conducted to examine the effects of phosphorus deficiency on energy status and functioning of soybean nodules. Phosphorus deficiency decreased ATP and total adenylate concentrations in and energy charge and specific nitrogenase activity of whole nodules. The bacteroid content per unit nodule mass and the distribution of total nitrogen and total phosphorus among the bacteroid and host cell fractions of nodules were not affected by phosphorus deficiency. Long term phosphorus-deficiency did not affect the energy charge and ATP concentration in the bacteroid fraction, whereas, these parameters decreased significantly in the host plant cell fraction. Energy charge and ATP concentration in the bacteroid fraction did not change during onset of and recovery from phosphorus deficiency. Conversely, energy charge and ATP concentration in the host plant cell fraction decreased significantly during onset of phosphorus deficiency and increased significantly during recovery from phosphorus deficiency. These results suggest that phosphorus deficiency decrease the specific nitrogenase activity of soybean nodules by inhibiting an energy dependent, reactions) in the host plant cells of nodules.