Nitrogen fixation, nodulation, and organ dry weights of soybean infested with the larvae of the southern corn rootworm,Diabrotica undecimpunctata howardiBarber, were estimated under controlled conditions. Larval southern com rootworm reduced the nitrogen-fixing activity of mid-vegetative and early reproductive soybean,Glycine maxMerrill. Soybean of both stages responded to the infestation and subsequent injury by increasing nodulation and organ dry weights of below-ground tissues relative to above-ground tissues. Infestation increased the dry weight of small nodules on vegetative plants and caused a 78.6% increase in the total number of nodules on R5 plants. Leaf area as well as leaf and stem dry weight was reduced in vegetative plants by infestation.