In a laboratory experiment, Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) seedlings had similar disease ratings when treated with known Fusarium isolates or concurrently with Fusarium and Streptomyces griseoviridis. When tested under greenhouse conditions and against known Fusarium isolates, more seeds germinated and survived as seedlings in control medium than survived in S. griseoviridis-inoculated medium or when S. griseoviridis and Fusarium were added together. A series of applications of S. griseoviridis as a soil drench to a crop of Douglas-fir seedlings did not affect seedling morphology. However, against resident levels of Fusarium, S. griseoviridis reduced Fusarium infection by 16%, but increased infection by F. oxysporum and F. proliferatum, two potentially pathogenic fungi, by 40%.