Twelve-week-old Douglas-fir seedlings in soil previously fumigated with Vorlex (20 percent methyl isothiocyanate, 80 percent chlorinated C3 hydrocarbons) without a gas-tight surface seal had more ectomycorrhizae than control seedlings in nonfumigated soil. Mycorrhizae on these control seedlings were more abundant than on comparable seedlings in soil previously fumigated with Dowfume MC-2 (98 percent methyl bromide, 2 percent chloropicrin) beneath a plastic cover. Fertilization with urea (200 kg N/ha applied before sowing of seed) resulted in fewer tomentose mycorrhizae on 20-week-old seedlings than were formed in nonfertilized soil or soil fertilized with treble superphosphate (200 kg P/ha). The abundance of smooth ecto-mycorrhizae on 20-week-old seedlings was not affected by the fertilizers. Inoculation of 5-week-old seedlings with fresh mycorrhizal roots of Douglas-fir caused an increase in number of mycorrhizae but no increase in weight over controls during a 15-week term. Dry weights of seedlings and the frequency of tomentose mycorrhizae were greater in soil used 4 years for Douglas-fir monoculture than in soils in the same nursery formerly used for agricultural crops. The development of a characteristic soil microflora with the first Douglas-fir crop is suggested as responsible for better growth and mycorrhiza formation in subsequent crops. Forest Sci. 20:57-63.