The presence, in the tallgrass prairie of North America, of an introduced European earthworm, Aporrectodea turgida Eisen (Lumbricidae) and native worms of the genus Diplocardia (Acanthodrilidae) led us to ask how the two groups compare with regard to mineralization of nitrogen and stimulation of plant growth in this ecosystem. Our working hypothesis was that earthworm- caused increases in N mineralization would be detected in leachates from pot cultures and reflected in increased plant growth and N uptake by Andropogon gerardii Vitman, a tallgrass dominant. The magnitude of both of these effects was expected to be greater in pots containing A. turgida, because these worms are larger and appear to be more active. Gut analysis was also performed to assess potential differences in feeding habits of the Diplocardias and A. turgida