The design of an X-ray double beam monochromator for digital subtraction angiography using synchrotron radiation is described. The monochromator provides two line-like monochromatic beams with a quanta energy just above and below the K-absorption edge of iodine. The monochromatization is performed by two flat silicon crystals in Laue diffraction on the (111) plane. The experimental results of testing the monochromator using synchrotron radiation from the VEPP-3 storage ring are also presented.