We have developed a transport equation for electronic transport in liquid or amorphous metals. This is used to investigate the effect of atomic motion on quantum interference (or weak localization) effects. Quantum interference is shown to exist in the liquid state even though elastic scattering is replaced by quasielastic scattering due to atomic diffusion. The interplay between elastic and inelastic scattering is investigated and the dephasing time is defined in terms of the dynamical structure factor S(q,\ensuremath{\omega}). A rough calculation for liquid Al shows that quantum interference effects in the liquid state are comparable with those measured in amorphous metals.