Developmental changes in the synthesis of root-hair proteins were followed in the symbiosis between the promiscuous legume Vigna unguiculata and the broad host-range Rhizobium sp. NGR234. Comparison of the two-dimensional electrophoresis patterns of proteins isolated from root hairs inoculated with wildtype or hair-deformation minus mutants revealed 12 symbiosis-specific proteins. Synthesis of three of these proteins was repressed 4 days after inoculation with Rhizobium. The remaining nine proteins were induced by Rhizobium 1, 2, or 4 days after inoculation. As three of these (15-, 31-, and 44-kDa hadulins) were specifically and transiently expressed in root hairs during the deformation process, we have named them hadulins (hair-deformation specific proteins). Five proteins (including 15- and 31-kDa hadulins) were first observed 24 hr after inoculation. Of these, only the 15-kDa hadulin was not induced by R. fredii USDA257Sl Nod⁺, Fix⁺ on V. unguiculata. Two days after inoculation, three additional proteins became apparent, while another (44-kDa hadulin) appeared on day 4. All 12 proteins seem to be associated with root-hair deformation and nodule development.