At Indian Head, Saskatchewan, there are plots that have been sprayed annually with 2,4-D for 36 years, since 1947. Herbicide application rates since 1969 in two sets of plots were 0.42 and 1.12 kg/ha, along with control plots with no application. The crop was wheat in a 3-year wheat – wheat – fallow rotation. The plots were monitored throughout the growing season in 1982 and 1983. The 14 most abundant species on these plots were grouped as susceptible, moderately tolerant, or highly tolerant to 2,4-D. These three groups differed significantly from each other with respect to the number of emerging seedlings during four separate time periods, survival to crop harvest, plant dry weight, and seed production. In all treatments, plant number and size decreased with emergence date, with only a few small plants emerging late in the season. Over the long term, 2,4-D use significantly reduced the number of plants of susceptible species, but it did not eliminate them. Reduced numbers of susceptible plants enabled the number of plants of highly tolerant species to increase. Even in plots treated with high rates of 2,4-D, plants of the susceptible species, Chenopodium album L. and Thlaspi arvense L., were still as abundant as those of any other species group. The overall effect of 2,4-D application was to reduce the difference in performance of susceptible and tolerant species, resulting in changes in quantitative aspects of community structure. No new major species has become established since 1947 as a result of 2,4-D application.