Studies of nitrogen metabolism in ectomycorrhizas have demonstrated that the fungal symbiont plays a fully integrated role in plant root metabolism and participates actively in the assimilation and transfer of newly absorbed nitrogen compounds by transferring amino acids. In symbiotic associations, such as mycorrhizas, location of the symbiosis ensures that mycelial growth of the fungus into soil provides access to nutrients in the soil solution. Changes in the distribution and activity of membrane-bound transport proteins in response to symbiotic interactions need to be investigated. In recent years several genes from H. cylindrosporum and P. pinaster, putatively involved in the nitrogen uptake and/or transfer, have been isolated or characterised by functional complementation of yeast mutants. The current state of the art will be presented.