The human progenitor cell antigen (CD34) is selectively expressed on hematopoietic progenitor cells in the bone marrow. In either cryostat sections of snap-frozen skin, or formalin-fixed paraffin-embedded sections of normal skin, anti-CD34 monoclonal antibody immunostained vascular endothelial cells and perivascular/interstitial dendritic cells, particularly in the reticular dermis. A distinctive population of perifollicular spindle-shaped cells in the midportion of the follicle (ie, bulge area), which is the site of the putative hair follicle stem cells, were CD34 positive, as were spindleshaped cells in and around the eccrine glands accentuating their basement membrane zone. In patch/plaque- and tumorstage acquired immunodeficiency syndrome-associated Kaposi's sarcoma lesions, CD34 expression was present on both the proliferating endothelial cells as well as the spindleshaped stromal cells. CD34 positive endothelial cells and spindle-shaped stromal cells may play important participatory and supportive functions in both normal and diseased skin.