The orientational behavior of a thermotropic polybibenzoate exhibiting a low-ordered smectic mesophase has been studied by real-time simultaneous synchrotron X-ray diffraction and stress-strain or stress-relaxation experiments. It follows from the stress-strain test (conducted at 105 degrees C and with a nominal strain rate of 3.33 min(-1)) that during the initial elastic region and around the yielding point, exclusively anomalous perpendicular orientation is obtained, with the molecular axes perpendicular to the uniaxial deformation direction. However, at the end of the necking region and the beginning of the strain-hardening process, parallel orientation begins to be obtained, and its intensity increases with the strain hardening. The intensity and spacing of the smectic spots and the layer order parameters for the two kinds of orientation have been obtained from the corresponding radial and azimuthal integrations of the photographs. One interesting finding is the observation of a 4% maximum expansion of the smectic spacing for the parallel orientation. In the subsequent stress-relaxation experiment, very little influence has been found on the smectic regions showing perpendicular orientation, but a progressively better parallel ordering is observed with an intensity increase by a factor of 3.2, with a very important increase of the order parameter, and with a simultaneous decrease of the smectic layer spacing. This decrease shows a perfect match with the stress-relaxation curve, in such a way that the two magnitudes, stress and smectic spacing, can be fitted to stretched exponential KWW functions with rather similar parameters.