The present work deals with the influence of unsteady conditions during continuous casting on the product quality. In particular, the effect of mould level fluctuations in conjunction with clogging was studied with respect to macroscopic steel cleanness. Not discussed in the literature so far, there is only little knowledge about the quality reducing effects of mould level fluctuations. Especially focusing on the individual types of mould level fluctuations and their activators, blooms which showed irregularities during casting, were rolled to tubes and bars and inspected by ultrasonic. The detected discontinuities were further examined by scanning electron microscopy and the results were compared with the mould level fluctuations.