Resonant photoemission at the uranium 5d disorption edge has been used to determine the 5f emission in URu3, URh3, URu3B, and URh3B polycrystalline samples. The observed 5f band narrowing (from 2.0 to 1.5 eV as one goes from URu3 to URu3B, and from 2.8 to 1.1 eV for URh3 and URh3B respectively) is explained as due to a decrease in the f-d hybridization between uranium and rhodium (ruthenium) atoms.