AbstractThis paper reflects three years' experience on the part of two of the authors with the Philips PW 1220/C X‐ray fluorescence spectrometer in combination with the Philips software packages ‘X‐ray 21’ and ‘X‐ray 10’ for the analysis of molybdenum, tungsten and their alloys.Of the ten analysis programs developed, three are discussed in detail. They embrace the determination of main constituents in the region of 100 per cent as well as the determination of traces in the ppm range after trace‐matrix separation. For trace analysis the standard software had to be modified in order to measure several blanks and standards and to overcome other shortcomings in the original program. The arithmetical means of blanks and standards are used for the calculation of linear calibration functions. This new, more versatile X‐ray 10 software package extends the applicability of the standard X‐ray 10 system to trace analysis. It also proved advantageous for the analysis of minor constituents i