The adsorption of acid and dimethylamine salts of 2,4-D and dicamba was studied on Canadian prairie soils and various other adsorbents, using slurry-type adsorption experiments. The amount of adsorption of both the acid and dimethylamine forms of the two herbicides was minimal. The results were explained on the basis of dissociation of the acidic and dimethylamine salts to the respective anionic forms in the near-neutral prairie soils. This conclusion was supported by (1) the strong adsorption of these herbicides to the anion-exchange resin but not to the cation-exchange resin; (2) the strong adsorption of the 14C-dimethylamine cation to these soils; and (3) the leaching patterns of the 14C-dimethylamine salts of both herbicides from soils and resins. Only the anionic species were eluted from columns containing soils and cation-exchange resin whereas only the 14C-dimethylamine cation eluted from columns containing anion-exchange resin. Both forms of 2,4-D and dicamba were strongly adsorbed to activated charcoal, cellulose triacetate, and peat. There was little or no adsorption of these herbicides to montmorillonite and kaolinitic clays, cellulose powder, or wheat straw.