The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 degrees C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (X-m) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for X-m1 (first stage) ranged from 1.1 X 10(-2) mol kg(-1) for natural kerolite at 40 degrees C up to 5.1 X 10(-2) mol kg(-1) for ammonium kerolite at 10 degrees C and the values for X-m2 (second stage) ranged from 9.1 X 10(-2) mol kg(-1) for natural kerolite at 40 degrees C up to 14 x 10(-2) mol kg(-1) for natural kerolite at 10 degrees C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied. (c) 2005 Published by Elsevier B.V.