The application of new secondary refining techniques and non-metallic inclusion reduction techniques in steel production processes has greatly reduced the size and amount of nonmetallic inclusions remaining in molten steels and steel products. This makes the inspection of inclusions difficult. Here the main methods used for the characterization of inclusions in clean steels are reviewed. The influences of inclusions on the properties of steels are discussed. Statistical methods for the prediction of the maximum inclusion size in a large volume of steel are introduced. Methods based on the statistics of extremes are described in detail. The methodology for the practical application of these methods is described and the factors affecting the precision of the estimation are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.