The Bureau of Mines conducted research to determine the resistance of basic refractories to corrosion by ash slags that would result from the burning of coal and lignite in metallurgical operations. Basic refractories are of economic interest because they are from one-third to one-half as expensive as 90- to 99-pct-alumina refractories. Static tests were performed at 1,300 deg c and dynamic tests at 1,400 deg to 1,650 deg c to investigate the stability of refractory specimens in a slag environment. In alkali- containing lignite ash slags, in order of decreasing resistance, magnesite, magnesite-chrome, and chrome-magnesite refractories all had corrosion resistances equal to or better than 90- to 99-pct- alumina refractories. These basic refractories formed slag penetration layers in dynamic tests, which helped protect them from further attack. Chemically bonded basic refractories in general did not have as good a resistance to slag attack as did burned refractories of the same composition. In very acidic coal ash slag, a chrome-magnesite refractory containing 30 pct mgo plus a slag inhibitor and direct-bonded magnesite-chrome refractories with 60 pct mgo had good resistance to attack. Chrome-magnesite refractories (30 to 40 pct mgo) were moderately to severely attacked, and refractories with greather than 70 pct mgo, were severely attacked by this same slag.