Abstract: A method and an apparatus for the detection of slag co-flowing within a sam of molten steel being poured from metallurgical vessel, more particularly during continuous casting, makes it possible to detect even a small quantity of slag in the emerging flow of molten metal without requiring the removal of the shielding for the pouring stream, or without interfering with the pouring, by measuring changes in the electrical conductivity of the pouring system by means of electromagnetic fields. To this end, one or more transmitter coils and receiver coils are mounted fixedly around the pouring stream. The transmitter coils are fed with a current containing several frequencies, and the magnitude and phase position of the voltage induced in the receiver coils are evaluated frequency-selectively so as to increase the sensitivity, the measuring transducer being operated in a bridge circuit.