With the advances made in clean steel technology in recent times, most current techniques to quantify inclusion contents fail to provide relevant feed-back to process engineering. This is a particular dilemma in that the larger a defect, the more dangerous it is, and the harder it is to find as inclusion size distributions are log-normal. By employing a destructive, laboratory ultrasonic test procedure valuable insights into the frequency, the size distribution and the composition of large deoxidation products can be gained. In this context, large inclusions are in the intermediate size range normally not detected by microscopic or macroscopic methods. This ultrasonic technique also can be used to map and measure other defects as porosities at the billet stage with a precision previously not attainable. Additionally, a development of conventional step-down testing can be used to enhance the understanding of exogenous large inclusion sources and frequency.