Current information pertinent to scatter radiation for mammographic x-ray spectra is limited. Data presented by the National Council on Radiation Protection and Measurements (NCRP), the current shielding authority, are restricted to 50 kVp tungsten target spectra and contain several incompatibilities with the modern mammographic situation. The ratio of scattered to incident exposure was measured for two molybdenum target spectra (36 kVp, 30 microns molybdenum filtration and 49 kVp, 50 microns aluminium filtration). The maximum scatter ratio occurred at 150 degrees to the primary beam direction for both spectra; the values were (1.73 +/- 0.09) x 10(3) and (2.6 +/- 0.1) x 10(3) respectively for a field area of 400 cm2, a scattering distance of 1 m and a primary beam exposure distance of 1 m from the x-ray source. The results obtained differ significantly from NCRP based data presently used for mammographic shielding calculations. The consequences of these differences are discussed.