A coarse-grained Monte Carlo algorithm on a modified diamond lattice has been used to study the dependence of threading of cyclic poly(ethylene oxide) molecules by linear poly(ethylene oxide) chains in the melt on the mass fraction (X-c) and the size (N-c) of the cyclics. Both short-range interactions based on the rotational isomeric state model and long-range interactions from a discretized form of the Lennard-Jones (LJ) potential energy function are included. LJ parameters sigma and is an element of/k(B) of 3.76 Angstrom and 154 K, respectively, are estimated for the coarse-grained model. In addition, a method is presented for detecting threading of cyclics that have instantaneous conformations that significantly differ from a circle. The percentage of cyclic molecules threaded can be described as a linear function of X,. When the cyclics consist of 10 or less coarse-grained monomer units, the percentage of cyclic molecules threaded falls to less than 1%, which suggests that spontaneous threading of cyclics smaller than 30-crown-10 is impractical in the melt. In addition, multiple threading occurs in cyclics larger than 42-crown-14. A weak end effect causes a slight preference for threading near the chain end.