For the first time, comprehensive X-ray spectroscopic and X-ray photoelectron data have been obtained on the energy spectra of valence electrons in phosphides of the transition metal series: TiP, CrP, MnP, FeP, NiP. Analysis of the experimental data on the electronic structure of phosphides of 3d-metals in the TiPNiP series indicates that the mechanism of interaction of the M 3d-states occurring near the top of the valence band with the s,p-states of phosphorus in the following sub-bands resides in the latter being induced near the d-sub-band as a result of the M 3d-P 3s,p interaction with the density maximum of the nearest P 3p-states being oppositely shifted as the number of d-electrons of the metal increases. Analysis of X-ray spectroscopic and X-ray photoelectron data on phosphides of transition metals along with those of metals of groups I(Cu, Ag) and II(Zn, Cd), and comparison of these data with the results of similar studies involving sulphides and silicides of the same metals indicate that the occupancy and the associated position of the d-shell of the metal within the valence band are the determining factors as far as the mutual arrangement of energy sub-bands and the symmetry of respective states are concerned. © 1974.