Since the treatment technical parameters change from heat to heat and even in the course of a single heat, determination of the functional relationships of refractory wear to these parameters by methods of statistical analysis is possible only with a method providing measurement of refractory wear during each heat. Taking this into consideration the change in magnesium oxide content in the slag during the course of a heat was seleted as the criterion for evaluating refractory wear in the slag zone of the ladle. This choice is based on the fact that periclase--chromite refractories containing about 60% MgO are used in the lining of the ladle slag zone while, with the exception of lime with an MgO content of 1-2%, MgO is present in not one of the heat-forming and deoxidizing components added to the ladle for outside-the-furn ace treatment~ Consequently, an increase in magnesium oxide content in the slag during the course of the heat may be taken as a qualitative characteristic of the wear of the Periclase~chromite refractories. In this investigation statistical material accumulated from the moment of start up of a unit in 1977 was processed. The course of treatment of more than 300 heats of steel was