The aim of this study was to compare profiles of acid soluble proteins in roots of Pisum sativum L. cv. Frisson and non-mycorrhizal mutants (myc−) when infected by vesicular arbuscular mycorrhiza funghi. Quantitative and qualitative modifications were detected by native or SDS PAGE in the protein composition of acidic extracts of endomycorrhizal roots of myc⁺, nod⁺ wild type P. sativum and of a myc⁺, nod-mutant, as compared to uninoculated control plants or a myc⁻, nod⁻ mutant, whether this was inoculated or not with Glomus mosseae. In native PAGE two proteins, already present in extracts of non-mycorrhizal pea roots, were enhanced in G. mosseae-infected myc⁺ plants (nod⁺ or nod⁻). One protein which appeared after inoculation with G. mosseae or G. fasciculatum in the roots of all pea plants, including the myc⁻, nod⁻ mutants, may be associated with appressorium formation. Four new proteins were detected in root extracts of G. mosseae-infected myc⁻ peas (nod⁺ or nod⁻), as compared to the myc⁻, nod⁻ mutant or uninoculated controls. One of these was probably of fungal origin, since it was also found in G. mosseae-infected tobacco and leek roots. These plants showed protein modifications different to those in endomycorrhizal peas, suggesting host-specific responses. SDS PAGE revealed the presence of two polypeptides of about 25 and 35 kDa in endomycorrhizal roots of myc⁺ peas. None of the endomycorrhiza-related proteins detected in roots corresponded to those extracted from spores of different fungi. This study provides new evidence that different molecular modifications occur during successful (myc⁺ pea, leek, tobacco) and unsuccessful (myc⁻ pea) endomycorrhiza infections, some of which are host-determined and others related to the expression of the fungal genome.