The adsorption of diuron [herbicide] into soil was studied in the presence of several surfactants. Cationic surfactants increased the adsorption of diuron, while the nonionic surfactants tested did not. The maximum adsorption of diuron occurred when cationic surfactants Aliquat 204andAliquat221wereused. Two alkyl chains of 12 carbons attached to the quaternary nitrogen atom of the cationic surfactant appeared to be an important requirement in this process. Even though this adsorption of diuron was strong enough to resist leaching through the soil, the diuron was still available for absorption by plant roots.