Human mononuclear phagocytes have the remarkable capacity to secrete a wide range of products. The reverse hemolytic plaque assay was used to visualize and quantify the secretion of lysozyme, interleukin 1 or type-beta transforming growth factor by individual monocytes and macrophages. With this sensitive immunoassay, the release of these products by either freshly isolated monocytes, macrophages derived from monocytes in vitro, or activated peritoneal macrophages was detected in both the presence and absence of secretagogues. When coupled with immunocytochemistry for EBM/11, a monoclonal marker for human cells of the monocyte/macrophage cell lineage, functional heterogeneity was evident both in the amount of lysozyme, interleukin 1 or type-beta transforming growth factor released per cell, and in the number of EBM/11+ cells which secreted detectable levels of these products at any one time. In addition, there was a size-dependent heterogeneity among human monocytes and culture-derived macrophages in their ability to secrete interleukin 1 or lysozyme, respectively. We conclude that the secretory activity of individual mononuclear phagocytes is markedly heterogeneous VSports手机版. .