Large hybridization effects are observed in $4f$ resonant photoemission spectra of Pr and Nd transition-metal compounds that lead to energy splittings of several eV varying strongly with the composition of the compounds. The phenomena are described quantitatively in the framework of a single-impurity Anderson model. Large splittings of the $4f$ emission are obtained, if the energy position of the expected $4f$ electron-removal state coincides with maxima of the valence-band density of states. For the ${4f}^{n}$ ground states, admixtures of ${4f}^{n+1}$ states of the order of some percents are obtained.