Summary.Measurements were made of the effect of exchangeable cations on the adsorption of linuron and atrazine by an ion‐exchange resin, cellulose phosphate powder, bentonite and a peat soil. The cations studied were Ca2+, Ni2+, Cu2+, Fe3+and Ce4+. The results with linuron were consistent with the hypothesis that complex formation with exchangeable cations is a possible mechanism of adsorption. This was not so with atrazine due to complications arising from pH effects, and it seems unlikely that adsorption of atrazine by this process is significan