Formation of stacking faults in the near-surface region of Cr-Mn-Ni steels that shows the effect of transformation induced plasticity (TRIP) was investigated by means of in situ X-ray diffraction experiments during a tensile deformation of the samples up to approximately 9%. The X-ray diffraction measurements revealed simultaneously the phase transformation of the TRIP steel during its plastic deformation and the changes in the interplanar spacing of the diffraction lines of austenite. As the interplanar spacing in austenite is influenced both by the residual elastic lattice strain and by the stacking fault density, the crystallographic anisotropy of the cubic lattice parameter was employed to distinguish these effects. Despite a partial correlation between the cubic invariant, which describes the crystallographic anisotropy of the stress-induced lattice deformation, and the orientation factor of the stacking faults in austenite, which describes the effect of the stacking faults on the orientation-dependent shift of the X-ray diffraction lines, the crystallographic anisotropy of the lattice parameter of austenite was proven to be capable of tracking the formation of microstructure defects and of distinguishing individual microstructure defects from each other. The X-ray diffraction experiments were complemented by transmission electron microscopy, which allowed the different observed anisotropies of the cubic lattice parameter to be assigned to specific microstructure defects. (C) 2012 Elsevier B. V. All rights reserved.