The mass distribution of diesel fuel sprays close to the nozzle has been determined by using absorption techniques with a monochromatic, synchrotron X-ray beam. The measurements were highly quantitative, with a temporal resolution better than 1 mus. The radial mass distribution of the fuel can be well described by a Gaussian distribution near the nozzle. The calculated volume fraction of the fuel indicates that the so-called liquid core near the nozzle did not exist under the test conditions examined (20-80 MPa injection pressure, 0.3-0.6 ms injection duration). Rather, the bulk of the spray was composed of a liquid/gas mixture with liquid content not exceeding 50% by volume. The maximum-density region was found at the front edge of the sprays, where the fuel volume fraction can reach 80%, and was limited to a thin layer (1-2 mm) perpendicular to the spray axis. The penetration of the front edge was found to be nonlinear with respect to injection duration within 20 mm from the nozzle.