Brillouin light scattering was used to probe acoustic waves propagating with both longitudinal and transverse polarizations in the surface and the bulk of self-supported particle track-etched polycarbonate membranes with 15- and 80-nm nanopores. The recorded scattering line shape at gigahertz frequencies reveals changes in the surface waves of the membranes which are more pronounced for the 80-nm nanopores despite the low porosity (0.7 and 0.05%). Because the measured elastic constants (1.2 and 6.2 GPa) were found to compare very well with the values for thick polycarbonate film, modifications of the elasto-optical coefficients and/or the transparency might be the reason for the different scattering line shapes. (C) 2004 Wiley Periodicals, Inc.