We have calculated the anisotropic dielectric function for PdO and PtO using the linear-muffin-tin-orbital--atom-sphere-approximation method. The optical matrix elements are explicitly included in the calculations and we find that they play a significant role in determining the shape of the frequency dependence of the dielectric function and its anisotropy. Our calculated dielectric functions for PdO are compared with the recent data of Weber et al. The agreement is good although the calculations show more features than are observed experimentally and give a band gap that is too small by about 0.6 eV. For PtO there are no experimental data available. We conclude that for these two transition-metal monoxides an itinerant description of the d states is appropriate.