Résumé : We have studied mass-energy distributions (MED) of fission fragments using two projectile target combinations, 12C + 204Pb and 48Ca + 168Er, leading to the same compound nucleus 216Ra at the excitation energy E* ∼ 40 MeV. It has been found that the contribution of tine asymmetric mode in the case of the former reaction is 1.5%, and it is 30% in the case of the latter one. We connect such a sharp increase in the yield of asymmetric products in the 48Ca + 168Er reaction with the quasifission process, the MED of which have a clearly expressed shell structure. The characteristics of the fission fragment MED are of such a kind that they can be interpreted by analogy with the low-energy fission of heavy nuclei as a manifestation of an independent mode of nuclear decay which competes with the classical fusion-fission process. © 2003 MAIK "Nauka/Interperiodica".