The density of states at the Fermi level N(E F ) was determined from normal-state static magnetic-susceptibility measurements on a series of YNi 2 - x (Co/Cu) x B 2 C compounds. N(E F ) decreases for both Co and Cu substitution in a manner similar to that observed previously for the superconducting transition temperature T c . However, for a given value of N(E F ), T c is significantly higher for Cu than for Co substituted compounds. This indicates that, other than changing N(E F ), substitution also modifies the electron-phonon coupling strength.