Robustness of feedback stabilization is studied for causal linear time-invariant input-output systems defined on the full time axis Z. The signal space setting used includes also certain unbounded signals. This study has been possible due to the use of two-operator plant models Ay=Bu. This avoids the intrinsic difficulties of unbounded causal input-output plant mappings y=Gu on Z. The full time axis robust stabilization results obtained here are analogous to those on the semi-infinite time axis N in the finite-dimensional case. However, there are certain important differences between the full time axis results and the semi-infinite time axis results for infinite-dimensional systems even when two-operator plant models are used. (C) 2006 Elsevier Ltd. All rights reserved.