We studied the distribution of the proteinase inhibitor antileukoprotease (ALP) and lysozyme (LSZ) in normal human tissues by use of an immunohistochemical technique. ALP could be demonstrated in a variety of healthy tissues, generated by secretory cells in lacrimal, respiratory, proximal digestive, and genital glands, but not in the urinary tract, endocrine glands, or the hematological system. In lung, part of the non-ciliated cell population in membranous bronchiolar epithelium, as well as in respiratory bronchioles, stained positively for the inhibitor. The distribution of ALP and LSZ was parallel in most but not all of the tissues examined. The distribution of ALP around most of the external orifices of the human body is discussed in relation to its possible local physiological role in defense against inflammatory reactions. The widespread parallel distribution of LSZ, a bacteriolytic agent, suggests a complementary role to ALP in local defense.