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THE induction of nitrogen-fixing nodules in legume roots by soil bacteria from the genera Rhizobium and Bradyrhizobium is host-plant-specific. This specificity is expressed at an early stage of the infection process and results from multiple interactions between bacterial and plant products. Among these, it has been suggested that root lectin recognized by bacterial receptor molecules is an important determinant of host specificity^1,2. Lectins are carbohydrate-binding proteins and it is known that legumes belonging to different cross-inoculation groups produce lectins with different sugar-binding specificities³. We have tested this suggestion by introducing the pea lectin gene into white clover roots using Agrobacterium rhizogenes as a vector. The 'hairy' clover roots that result can be nodulated by a Rhizobium strain usually specific for plants from the pea cross-inoculation group.