We tested the hypothesis that elevated blood pressure, a known stimulus for vascular remodeling and an independent risk factor for the development of atherosclerotic disease, can modulate basal and cytokine-induced tissue factor (TF; CD 142) expression in cultured human endothelial cells (EC). Using a chromogenic enzymatic assay, we measured basal and tumor necrosis factor- (TNF-; 10 ng/ml, 5 h)-induced TF activities in human aortic EC (HAEC) and vena cava EC (HVCEC) cultured at atmospheric pressure and at 170 mmHg imposed pressure for up to 48 h. Basal TF activities were 22 ± 10 U/mg protein for HAEC and 14 ± 9 U/mg protein for HVCEC and were upregulated in both cell types >10-fold by TNF-. Exposure to pressure for 5 h induced additional elevation of basal TF activity by 47 ± 16% (P < 0.05, n = 6) for HAEC and 17 ± 5% (P < 0.05, n = 3) for HVCEC. Pressurization also enhanced TF activity in TNF--treated cells from 240 ± 28 to 319 ± 32 U/mg protein in HAEC (P < 0.05, n = 4) and from 148 ± 25 to 179 ± 0.8 U/mg protein (P < 0.05, n = 3) in HVCEC. Cytokine stimulation caused an ~100-fold increase in steady-state TF mRNA levels in HAEC, whereas pressurization did not alter either TF mRNA or cell surface antigen expression, as determined by quantitative RT-PCR methodology and ELISA. Elevated pressure, however, modulated the EC plasma membrane organization and/or permeability as inferred from the increased cellular uptake of the fluorescent amphipathic dye merocyanine 540 (33 ± 7%, P < 0.05). Our data suggest that elevated static pressure modulates the hemostatic potential of vascular cells by modifying the molecular organization of the plasma membrane.