The effect of four polyamines, putrescine, cadaverine, spermidine and spermine, on arbuscular mycorrhizal (AM) infection by Glomus intraradices was tested on Pisum sativum, cv. Frisson (nod⁺myc⁺) and two isogenic mutants of this cultivar, P56 (nod^–myc⁺) and P2 (nod^–myc^–). Polyamines were applied at 0 and 5.10^–4 M as soil drenches. Endomycorrhizal infection parameters were measured 3 weeks after inoculation. Polyamine treatment significantly increased the frequency of mycorrhizal infection in the myc⁺ pea lines (cv. Frisson and P56) and the number of appressoria formed in the myc^– line (P2). A positive correlation was found between polyamine chain length and their stimulation of fungal development. Results are discussed in relation to the possibility that polyamines may act as regulatory factors in plant-AM fungus interactions.