To date, 34 species of primary parasites have been recovered from the spruce bud worm ( Choristoneura fumiferana (Clem.)) in Oregon. Of these, 15 species are considered of major importance. Analysis of the abundance and distribution of these parasites was based on concepts and methods used in plant sociology. Within host populations during the period 1953-56, seven species are shown to have increased in density without decreasing in presence, and three species to have increased in presence without decreasing in density . .For one infestation, the frequency of parasite species over the area was found to be consistent with density. Whereas most species are believed to be distributed over the region, it is obvious that conditions within a single infestation may be unfavorable to the multiplication of some species. Secondary parasitization is suggested as a factor retarding the increase in density of primary parasites during the early stages of an outbreak.