The number and distribution of lysozyme and S100 immunoreactive cells were analyzed in ten cases of lymph node sarcoidosis. Three phases of granuloma development could be differentiated, each showing a typical immunohistological pattern. The early small granulomas consisted of lys- or very weakly lys+ mononuclear phagocytes and developed within an area of focalized accumulation of S100+ antigen-presenting cells. The mature large granulomas were composed of polygonal epithelioid cells with abundant cytoplasm showing very strong granular lysozyme positivity. S100+ cells could still be observed, mainly around the granulomas, but in diminished number. In the final fibrozing phase the epithelioid cells lost their lysozyme immunoreactivity and no S100+ antigen-presenting cells were present within or around the granulomas. In one patient granulomas with central necrosis and palisading, lys- epithelioid cells were also observed, possibly representing a different microenvironment (antigen/antibody equilibrium?). The change in the pattern and number of lysozyme and S100 immunoreactive cells probably reflects the development of the granulomas and is related to the activity of the disease.