The expression of different lineage-specific markers was examined on tissue-derived fibroblast cultures in three species (mouse, rat and human), using indirect immunofluorescence or labelled streptavidin-biotin techniques. Smooth muscle cells and a human monocyte-like cell line (U 937) were used as controls. Five monoclonal antibodies against human fibroblast epitopes et two against mouse fibroblasts were selected during this screening on cell cultures. Three surface markers (Thy-1, 6-19 and 1B10) and, particularly, one (5B5) cytoplasmic marker of human fibroblasts were suitable for labeling frozen, but not paraffin-embedded, tissue sections. Unfortunately, the two mouse fibroblast markers appeared of difficult and limited interest for this histopathologic strategy.