Monoclonal antibodies were used to detect infection thread glycoproteins (MAC 204, MAC 236, MAC 265) and arabinogalactan proteins (AGPs) (JIM 8, MAC 207) in roots of nod⁺ myc⁺ pea (Pisum sativum L.) and an isogenic nod⁻ myc⁻ pea mutant, inoculated with Glonius mosseae (Nicol. & Gerd.) Gerd. & Trappe. MAC 236 and MAC 207 gave strong responses for extracts of all roots in a dot immunobinding assay (DIBA) and were used for immunogold localization of corresponding antigen in root tissues. MAC 236 antigen accumulated in wall appositions induced by the mycorrhizal fungus in outer root cells of the resistant nod⁻ myc⁻ mutant, but not in epidermal cells of nod⁺ myc⁺ plants. In the latter, MAC 236 antigen was localized in wall material deposited around hyphae penetrating parenchyma cortical cells and around large branches of intracellular arbuscules, but not in the interfacial material or on the host membrane surrounding more finely branched arbuscule hyphae. The antigen accumulated again around wall remains of senescent hyphae. MAC 207 labelled plant plasma membrane, and antigen was also localized in wall appositions below appressoria in epidermal cells of the nod⁻ myc⁻ mutant, together with β-1,3 glucans detected using a monoclonal antibody. The epidermal cell wall of nod⁺ myc⁺ roots was unreactive to MAC 207 but related AGP was associated with the interface between the fungal wall and host membrane at all stages of arbuscule development in parenchyma cells of nod⁺ myc⁺ plants.· The possible role of these different molecular components in cellular interactions between the fungal symbiont and root tissues in the nod⁺ myc⁺ and nod⁻ myc⁻ plants is discussed.