Refractory products greatly affect steel quality and cleanliness. Some examples of interactions between refractories-slag-steel on steel desulfurization and carbon pick up in ultra-low carbon steel during the secondary treatment processes are presented. Consequences of refractory behaviour with respect to liquid steel cleanliness during continuous casting are examined : reoxidation of the metal, transfer of elements in the tundish, alumina clogging, etc. Methods for further improvements are indicated.