Abstract: The invention relates to a method and an equipment for determining the content of an element from a flowing sample mass (1) by utilizing x-ray fluorescence, in which method the sample mass (1) is irradiated with x-ray or gamma radiation; the radiation emitted by the sample mass is detected; an energy-dispersive radiation spectrum of the radiation emitted by the sample mass is determined; and the content of the element is determined from the measured radiation spectrum on the basis of the intensity of the radiation spectrum window characteristic of this element.