The presence and localization of the marginal zone (MZ) in the human lymph node is controversial. The authors analyzed the distribution of sIgM+sIgD− MZ lymphocytes (MZL) expressing alkaline phosphatase (ALP) activity in a series of reactive lymph nodes and spleens with the use of immuno- and enzymehistochemistry, and a combination of both technics. MZL were found scattered in lymphocytic coronas composed of densely packed, small, round lymphocytes. In the lymphocytic coronas showing prominent zonal layering into an inner, densely packed rim and outer, loosely arranged rim, the latter area proved to be composed of sIgM+sIgD−ALP+ MZL, in contrast to the inner rim, which was composed of sIgM+sIgD+ALP− small, round lymphocytes. It is concluded that the human reactive lymph node, like the spleen, contains MZL. These MZL apparently belong to a dynamic B-cell compartment, the morphologic expression of which may vary from scattered singular cells hidden in the lymphocytic corona to a clearly recognizable peripheral rim of medium-sized lymphoid cells.