The natural gamma-radiation technique was used for the first time in Spain in an underground mine in the region of Asturias. The objective was to determine the ash content of run-of-mine material (ROM) loaded in wagons coming from various layers of the mine. The information obtained can be used to adjust the mining operation accordingly. The results showed that this technique can be used with good accuracy. The mean residual error is +/-3.2% ash content and their standard deviation is 1.9% ash for a wide range of load conditions. (C) 2002 Elsevier Science B.V. All rights reserved.