Background: Antibody validation for tissue staining is required for reproducibility and criteria to ensure validity have been published recently. The majority of these recommendations imply the use of routinely processed tissue (FFPE). Materials & Methods: We applied to lightly fixed frozen sections a panel of 126 antibodies validated for FFPE with extended criteria. Results: Less than 30% performed conservatively with all fixations, 35% preferred one fixation over another, 13% gave non-specific staining, 23% did not stain at all. Conclusions: Individual antibody variability of the paratope fitness for the fixed antigen may be the cause. Re-validation of established antibody panels is required when applied to sections whose fixation and processing is different from the tissue where they have been initially validated. These are supplementary Data to the manuscript. In addition Tabel 1 and Supplementary Table 1 are provided in Excel format.