It is shown that petrographic methods, using the microscope and micro-refractometer, can be a valuable aid in the identification of non-metallic inclusions in steel, even when their size is only a small fraction of a millimetre. Special ways of preparing the samples are given, and some of the methods used in examination are indicated. Natural chromite, corundum, merwinite, mutlite, quartz, rhodonite, spincls, and zircon are taken as examples of the minerals found.