A lithium niobate optical parametric oscillator pumped by a Nd:YAG laser has been injection seeded with a continous-wave diode laser. Injection seeding was achieved over signal wavelengths ranging from 1.526 to 1.578 microm, with a corresponding range for the idler of 3.26 to 3.51 microm At a signal wavelength of 1.535 microm, 7.6 mJ of signal radiation was generated from a pump energy of 75 mJ, with a measured bandwidth of 0.18 GHz.