A new method is proposed for nanoscale hard x-ray measurements. This method uses a reflection on a heavy-metal wire that functions as a single slit with a nanoscale aperture for a parallel x-ray beam. This "nanoslit" can be used to perform high-spatial-resolution measurements of the intensity distribution of a wavefront that diverges from an aperture. In experiments, Fresnel fringes generated by a rectangular aperture were measured using a 300-mu m-diameter platinum wire as the nanoslit. In these experiments, the finest fringes with a period of 26 nm could be successfully resolved. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456447]