For hole doped high-temperature superconductors (HTS) there is only little
doubt left that the superconducting order parameter is of d(x2-y2) wave typ
e. Several methods of phase sensitive measurements of the superconducting o
rder parameter yield convincing and consistent results in case of the hole
doped HTS. For the electron doped HTS there has been mounting experimental
evidence for s-wave type order parameter symmetry, however, very recent mea
surements are discussed as evidence for d(x2-y2)-wave symmetry. In this pap
er we summarize the contradictory experimental situation with respect to th
e symmetry type of the superconducting order parameter in electron doped HT
S. The results from phase sensitive tunneling measurements and London penet
ration depth measurements are discussed together with the new results of tr
icrystal junction experiments. Additional experiments to solve this importa
nt issue. as for example investigation of doping dependence and superconduc
ting quantum interference experiments are suggested. (C) 2001 Elsevier Scie
nce B.V. All rights reserved.