Human peripheral blood mononuclear cells from healthy donors were treated ex vivo with the proteolytic enzyme bromelain and studied by flow cytometry. Bromelain-treated lymphocytes exhibited 60–90% reduced cell surface staining for CD44 and CD62-L molecules. While the staining for molecules CD 16, CD56 and CD49d was unaffected, a moderate increase (10–40%) in expression of the β2-integrins CD1 la-c was seen. This selective modulation of cell adhesion molecules (CAM) was seen on T cells and NK cells, as well. The selective modulation of CAM may help explain some of the clinical effects observed after bromelain treatment in patients suffering from chronic inflammatory disease, HIV and cancer.