Changes in polypeptide contents following inoculation of roots of Pisum sativum L. (wild type cv. Frisson (myc+, nod+)) with the arbuscular mycorrhizal fungus Glomus mosseae were analysed by two-dimensional gel electrophoresis (2D-PAGE). A different polypeptide pattern was obtained in a mycorrhiza-resistant pea genotype P2 (myc-, nod-) inoculated with G. mosseae. In order further to characterize the polypeptide modifications detected and to provide evidence for some possible symbiosis-related (SR) proteins, a time course experiment, from appressoria formation to fully developed symbiosis, was carried out on two genotypes allowing fungal colonization: the wild type and its isogenic mutant P56 (myc+, nod-). The same experiment was done with the mycorrhiza-resistant pea genotype (myc-, nod-). After G. mosseae inoculation, we characterized 12 additional polypeptides in the two mycorrhiza-compatible pea genotypes which were never observed in root extracts from the mycorrhiza-resistant mutant. Five polypeptides were first detected in the early stage of the symbiosis (5 d of inoculation) while others were observed later (8 d of inoculation). The induction and accumulation of these polypeptides seem to be more correlated to the establishment of the functional symbiosis than to the recognition stages and appressorium formation. Furthermore, none of the additional polypeptides were detected in the mycorrhiza-resistant pea genotype. This mutant was more characterized by a great repression of polypeptides. In addition, up-regulated and down-regulated polypeptides from the mycorrhiza-compatible genotypes were different from those of the mycorrhiza-resistant genotype.