We have identified the following polyamines in root exudates of pea: putrescine, cadaverine, spermidine, spermine, phenylethylamine and 3-hydroxy,4-methoxyphenylethylamine. Putrescine and spermidine had a stimulating effect on in vitro spore germination and hyphal growth of Glomus mosseae. Putrescine, cadaverine, spermidine and spermine stimulated endomycorrhizal infection of pea in vivo. We found a positive correlation between polyamine carbon chain length and the extent of enhancement of the endomycorrhiza development.