Electron paramagnetic resonance (EPR) spectroscopy and X-ray diffraction (XRD) studies were carried out on synthetic diamonds prepared using nickel, invar and monel as the catalyst solvents at high temperature and high pressure. Nitrogen and nickel were found to be the main impurities present in these specimens. -Quartz and copper phases were also observed in some cases. The width of EPR hyperfine lines of nitrogen atoms was found to depend on the catalyst solvents used in the synthesis. These studies show that EPR and XRD techniques yield complementary results about the defects/impurities present in synthetic diamonds.