The water and salt transport properties of untreated and heat-treated poly(vinyl alcohol) (PVA) membranes were investigated. Water and salt permeabilities decreased abruptly as a result of heat treatment. The effect of heat treatment on the water and salt transport in PVA is expressed mainly by changes in the activation energies of the corresponding permeability co efficients. Due to the fact that the decrease in the salt permeability with heat treatment was considerably greater than the decrease in the water permeability, a pronounced improvement in the salt rejection of PVA membranes was found as a result of heat treatment. T.T.D. (02129/82) and M.A.K. -- AATA