Inflammation, thrombosis, and immunity involve close interactions between leukocytes and vascular endothelium. Endothelial cells represent both targets and producers of lymphokines. Our study was designed to define the capacity of human endothelial cells (HEC) to produce a novel, recently purified, and molecularly cloned monocyte chemotactic and activating factor. This factor has been identified in the culture supernatants of tumor cell lines (tumor-derived chemotactic factor (TDCF)) as well as activated monocytes and fibroblasts (monocyte chemotactic and activating protein, MCAF, or monocyte chemoattractant protein-1, MCP-1). IL-1 induced high levels of production of chemotactic activity for monocytes in culture supernatants of HEC. IL-1-treated HEC expressed high levels of MCAF/MCP-1/TDCF mRNA transcripts, as assessed by Northern blot analysis. TNF and LPS, unlike IL-6, also induced MCAF/MCP-1/TDCF gene expression. Nuclear run off experiments revealed that IL-1-activated transcription of the MCAF/MCP-1/TDCF gene. The production of MCAF/MCP-1/TDCF may represent one of the mechanisms whereby endothelial cells, exposed to inflammatory signals, participate in the regulation of leukocyte extravasation. Production of this cytokine by vascular cells may in particular be relevant under conditions of selective extravasation and activation of mononuclear phagocytes.