Crystal impedance and electrochemical measurements were used to demonstrate that compact and rigid poly(N-vinylcarbazole) (PVCz) films may be obtained from anhydrous acetonitrile solutions, provided that the polymerisation potential is relatively low and the bath solution is enriched in H+ ions. Electrochemical quartz crystal microbalance studies of PVCz films led to the conclusion that the break-in process includes cross-linking between the polymer chains via the vinyl groups with irreversible incorporation of anions. The apparent diffusion coefficients obtained for transport of ions through the film during reversible oxidation and irreversible cross linking of the polymer are, respectively, 6 x 10(-10) cm(2) s(-1) and 2 x 10(-10) cm(2) s(-1).