An automatic computerized ultrasonic cleanliness rating system for measuring nonmetallic inclusion content of semifinished materials such as steel billets is described and discussed with regard to its function and reliability. Correlative studies relating inclusion areas as measured by light microscopy and magnetic particle inspection were within reasonable agreement with inclusion areas assessed ultrasonically.To further provide design engineers with material quality acceptance standards that are related to mechanical behavior, mechanical tests were performed on high strength (280 ksi ultimate) steel exemplifying various ultrasonic cleanliness levels. A significant impairment in ductility (percent reduction of area) is encountered with increasing ultrasonic inclusion severity. Uniaxial fatigue under unidirectional and reversed loading conditions is markedly influenced in proportion to the ultrasonic signature number. Impact and fracture toughness parameters are sensitive to a lesser degree.