We will study time dependence of interchain contacts in entangled and unentangled polymer melts. We find that "clusters" of contacts in entangled melts persist in time up to at least 0.2 of the longest relaxation time. The clusters of contacts in un-entangled melts disappear and reappear on at least two orders of magnitude shorter time scale. We also examine time-dependent correlation functions that try to quantify the properties of contacts. (C) 1997 American Institute of Physics.