The pervaporation behaviour of chlorinated hydrocarbons (ClHC's) was studied in detail. The permeability of different ClHC's through a hydrophobic membrane was considered in relation to their molecular structure and some of their physicochemical properties. The hydrocarbons selected for this study differed in: the number and position of chlorine atoms, the chain length, the degree of branching and the presence of a double bond. The membranes were composite membranes: a dense top layer consisting of PDMS (polydimethylsiloxane), filled with hydrophobic zeolite on a layer consisting of porous PAN (polyacrylonitrile) on polyester fabric.