The ectomycorrhizal association between Mountain Pine (Pinus mugo) and the fungus Suillus luteus has been studied in an attempt to promote establishment and growth of trees on high altitude revegetation sites. In vitro growth studies of S. luteus showed it was capable of growing at low phosphorus levels and utilising a variety of carbohydrate substrates. A number of organic acids, components of root exudates, stimulated fungal growth. Basidiospores have the greatest potential for pine seed inoculation. Investigation of the viability, storage and germination of these spores revealed that frozen or cool stored spores and freeze dried hymenial tissue were the best forms of inocula. Basidiospore viability was best determined by acridine orange staining with fluorescence microscopy. Nicotinic acid and inositol stimulated spore germination although germination levels were always low. Large numbers of basidiospores were necessary to obtain good mycorrhiza formation on seedlings and the inocula lost effectiveness with long storage periods. A scanning electron microscope study of the mycorrhizal infection process showed the presence of novel 'vesicular bodies', closely associated with the Hartig net. Granulated seeds containing a basidiospore inoculum were prepared and seedlings developing from these possessed low levels of mycorrhizas.