Integrally-skinned asymmetric polyamide-6 membranes were prepared by casting 15 wt.% solution of polymer in 85 wt.% formic acid onto a glass plate and precipitation in water at 4 degrees C. The obtained membranes were dried for 1 h at different temperatures ranging from 25 to 140 degrees C in air and from 25 to 200 degrees C in vacuum, respectively. The pervaporation separation properties of such treated membranes were studied with binary water-2-propanol mixtures consisting of 5 to 95 wt.% water. The membranes showed water permselectivity over a wide range of the feed composition. Thereby the water permselectivity reached a maximum at low water contents in the feed mixture. The selectivity was improved by thermal treatment of the membranes at temperatures above the glass transition temperature T-g of polyamide-6 (approximate to 60 degrees C). However, the permeate flux decreased with increasing drying temperature due to the removal of entrapped water from amorphous domains, the formation of new crystalline domains and the decrease of the pore size and of the specific surface area during the thermal treatment. These effects were confirmed by dsc measurements, X-ray scattering experiments and BET measurements.