The mucosal surface of the human urothelium represents a very large exposure area to exogenous agents, including potentially harmful microorganisms. Male human urothelium was treated for the immunohistochemical demonstration of secretory IgA (sIgA) in order to verify its own possible antimicrobial properties. An intense immunoreactivity for sIgA was observed in the apical cells of the urethral and vesical epithelia. The ureteric epithelium, at the luminal surface, showed discontinuous areas of less dense or completely absent reaction product. A less intense immunoreactivity was observed in the pelvic apical epithelial cells. The results suggest that sIgA play a prominent role in the local defence mechanisms of the lower urinary tract against ascending infections, whereas in the upper urinary tract the immuno-specific local defences seem reduced.