Endotoxin (LPS) and interleukin-1 beta (IL-1 beta) increased the expression of tissue factor, a membrane-anchored glycoprotein that initiates blood coagulation on the surface of cultured human umbilical vein endothelial cells (HUVEC) and human monocyte/macrophages. On monocyte/macrophages, oleic acid strongly inhibited LPS-induced tissue factor expression, a similar activity also being obtained with regard to the pyrogenic effects of IL-1 beta. Other polyunsaturated fatty acids such as linoleic or linolenic acid also reduced tissue factor expression whereas palmitic acid was ineffective. In contrast, these compounds showed no effect on LPS- or IL-1 beta-induced tissue factor expression in HUVEC when tested at the concentration of 10 microM. These data therefore suggest that the well-recognized antithrombotic and antiatherogenic effect of polyunsaturated fatty acids may in part be mediated through an inhibition of tissue factor expression in monocyte/macrophages.