Both polyanions and polyampholytes cause the dissociation of DNA-polycation complexes in experiments. To elucidate their mechanisms, Monte Carlo simulations have been conducted on a simple model, with DNA modeled as an infinite charged cylinder and other polyions treated as charged Shish-Kebab rods. Our results show that a highly charged polyanion is required to separate a polycation from a DNA. However, for a diblocked polyampholyte, its net dipole induces a higher probability to bridge a DNA and a polycation. Thus, the loosening mechanisms are found to be markedly different between polyanions and polyampholytes. (C) 2007 Elsevier B.V. All rights reserved.