The Bureau of Mines investigated the effect of refractory oxide additions, introduced in soluble form, on the high-temperature properties of 90- and 98-pct-mgo brick. Brick samples were soaked in solutions containing al, ca, cr, CO, fe, mg, mn, mo, ni, si, sr, sn, ti, or zr ions. Additions to 98-pct-mgo brick did not generally result in statistically significant property improvements. Statistically significant improvements were noted in hot modulus of rupture (mor), slag resistance, and spalling resistance of the 90- pct-mgo brick for additions of al, mg, or sn. High-temperature performance of treated 90-pct-mgo refractories was equal to or approached that of 98-pct-mgo brick. The marked improvements due to tin were obtained with additions of only 1.14 Wt pct sNO2. This report is based upon work done under a memorandum of agreement between the Bureau of Mines, U.S. Department of the Interior, and the University of Alabama.