The K x-ray absorption spectrum of manganese was studied in the borides and in the pure metal. The essentially linear change in the intensity of the initial absorption (a few electron volts above the Fermi boundary) is found to be in good agreement with the assumption that some of the boron valence electrons are transferred to the band of outer dsp states of the metal. There is a discussion of the relation between this effect and various physical properties of the manganese borides.