To test the effect of seed treatment with fungicides on the development of mycorrhizal fungi, bean seeds were treated with fungicide dry or vehicled in the organic solvents, ethanol or dichloromethane and then planted in soil inoculated with the mycorrhizal fungus Glomus macrocarpum and/or the plant pathogenic fungus Fusarium solani. Measurements were made at 4 day intervals, to assess the presence of mycorrhizae or disease in the roots as well as top dry weight, root fresh weight and root length. Fungicidal seed treatment did not affect the initial occurrence of mycorrhizae, number of spores of G. macrocarpum in the soil or root length. Fresh weights of roots and dry weights of tops were greater in the presence of the mycorrhizal fungus. The onslaught of symptoms by F. solani was significantly retarded by treatment with fungicides plus mycorrhizal fungi or fungicides plus organic solvents.