Previous studies have suggested that corneal stromal keratocytes express the CD34 antigen. We wished to investigate CD34 antigen expression in normal mouse cornea using dualand triple-staining techniques. Whole-mount preparations of mouse and rat corneas were examined with confocal microscopy using single, dual, or triple immunostaining to study their morphology, phenotype, and distribution. Single-cell suspensions from normal mouse corneas were also prepared and analyzed by flow cytometry. After short-term culture of corneal stromal explants, nonadherent cells were harvested and cytospins were prepared and stained for different markers.Combined staining for F-actin and leukocyte differentiation markers clearly showed that the corneal stroma contains a population of CD45 + resident bone marrow-derived cells, whereas most cells were CD45-