An immunocytochemical screening using polyclonal and monoclonal antikininogen antibodies was performed in various human tissues including blood cells. By comparing the spatial relationship between the cellular localizations of tissue kallikrein and kininogens it was evident that in some tissues both enzyme and substrate were present establishing a close anatomical relationship whereas in others only one of the components could be detected. This pattern of distribution suggests that within various tissues (cells) the major function of either tissue kallikrein (kininogenase, processing enzyme) or kininogen (kinin precursor, cysteine protease inhibitor, kallikrein acceptor molecule) could be different and probably specific to each cell type.