The effects of gamma-irradiation on the methanol diffusion behaviour in polycarbonate have been investigated by UV-visible, Fourier Transform Infra-red (FTIR) Spectroscopy, Positron Annihilation Lifetime Spectroscopy (PALS), Differential Scanning Calorimetry (DSC), Sorption, and Optical Microscopy. Positron results show that the free volume size and its content decreases after gamma-irradiation which is due to cross-linking of chains. The cross-linking process is further confirmed by DSC measurements, which indicate an increase in glass transition temperature (T-g) after gamma-irradiation. Sorption results reveal that methanol diffuses faster in virgin polycarbonate as compared to cross-linked polycarbonate (after gamma irradiation) in agreement with the results of supplementary techniques. Interestingly, the optical microscopic examination of the sample surfaces provides clear evidence of decreased micro-crack formation in gamma-irradiated polycarbonate as compared to the virgin sample. This decrease in crack formation can be related to the decrease in the rate of methanol diffusion. (C) 2003 Kluwer Academic Publishers.