The adsorption of the plant growth regulator chlorocholine chloride from aqueous solutions by homoionic montmorillonitesof K+, Ca2+, Mn2+, Co2+, and Ni2+takes place through a reversible cationic exchange and by a coadsorption onto the external surface of the silicate. The isotherms fitted Langmuir's equation, and the total retention capacity was close to the CEC (106 meq/100 g), although some 20% of the exchange cations were not displaced by the chlorocholine ion. Data from the x-ray powder diffraction and infrared studies showed that the chlorocholine molecule was adsorbed in the interlamellar spaces; it had neutralized the layer charge and was oriented so that the quaternary ammonium ion C3axis was perpendicular to the silicate layers.