Based on previous Bureau of Mines research indicating that improved high-temperature properties could be achieved for periclase refractories through chemical additions, the Bureau investigated the properties of full-size bricks produced from chemically modified periclase refractory grains and the suitability of making such chemical additions to mg(oh)2 slurries prior to production of the periclase grains. In full-size brick testing, strength values, both hot and cold, for the optimized bricks were superior to those for a commercial 98-wt-pct-mgo refractory. The best results were obtained for a natural magnesite with an adjusted cao:sio2 (c:s) ratio of 3.0 and a 1.0-wt-pct addition of zro2 and for a seawater periclase with an adjusted c:s ratio of 2.5 and a 0.5-wt-pct addition of mNO2. For samples produced from chemically modified mg(oh)2 slurries, additions of both mNO2 and zro2 and an increase in c:s ratios produced significant increases in hot flexural strength, similar to those resulting from chemical additions made to periclase grains. The most effective modifications were additions of mNO2 to brine- derived periclases having a c:s ratio adjusted to 3.0. These results on chemically modified magnesia refractories indicate that such material could potentially substitute for magnesia-chrome refractories containing imported chromite.