The self-energy responsible for the narrowing of the Ni 3d band as observed in photoemission data is obtained from a comparison of a calculated band structure with a band structure determined from photoemission data. The self-energy is found to depend on both wavevector k and band index n, but the authors are able to demonstrate that this dependence is almost exclusively introduced through the hybridisation with sp bands. The self-energy of pure d states is found to be linear, Sigma ( epsilon )=-0.44 epsilon , down to about 3 eV below the Fermi energy.