The pseudo-rapidity region 2.5 < |η| < 4.0 in ATLAS is a particularly complex transition zone between the endcap and forward calorimeters. A set-up consisting of 1/4 respectively 1/8 of the full azimuthal acceptance of the ATLAS liquid argon endcap and forward calorimeters has been exposed to beams of electrons, pions and muons in the energy range E ≤ 200 GeV at the CERN SPS. Data have been taken in the endcap and forward calorimeter regions as well as in the transition region. This beam test set-up corresponds very closely to the geometry and support structures in ATLAS. A detailed study of the performance in the endcap and forward calorimeter regions is described. The data are compared with MC simulations based on GEANT 4 models.