The distribution of various chlorinated compounds, 2,4- dichlorophenoxyethanoic acid, 2,4-D, 2-(2,4-dichlorophenoxy)propionic acid, 2,4-DP, 2,4,5-trichlorophenoxyethanoic acid, 2,4,5-T, 2-(2,4,5-trichlorophenoxy) propionic acid, 2,4,5-TP and 2,3,6-trichlorophenylethanoic acid, 2,3,6-T, was investigated in mutually saturated water-non-aqueous solvent systems at 298.15 K. The data were used to calculate (i) the distribution constant, Kd, referred to the process involving ionic species in the aqueous phase and undissociated species in the organic phase and (ii) the dimerisation constant, Kdim, in aprotic media saturated with water. A new treatment used to derive these data is described. The Kd values in the mutually saturated solvents for the various pesticides are compared with corresponding data in the pure solvents derived from solubility measurements in water and in non-aqueous solvents. Data in water were corrected for ion-pair formation while those in the organic phase were corrected for dimerisation. Good agreement is found between the two sets of data. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2005.