Computes realistic nucleon mean free paths in ¹²C and ²⁰⁸Pb nuclei by including the effects of Fermi motion, Pauli blocking and the Coulomb and nuclear interaction potentials. These local (i.e. radius-dependent) mean free paths can differ enormously from the nuclear matter value. The meaning of a mean free path in finite nuclei is discussed and an alternative quantity, the absorption probability as a function of impact parameter, is defined.