Cemented total hip replacement surgery is associated with intraoperative cardiorespiratory depression and postoperative proximal deep vein thrombosis which may be linked to an extreme intraoperative thrombin generation and local and systemic effects of monomethylmethacrylate (MMA) released into circulation from curing cement. This in vitro study demonstrates that MMA alone or in combination with thrombin have effects on monocytes and human umbilical vein endothelial cells (HUVEC) which modulate their procoagulant activities. Moderate doses of MMA had a slight tissue factor (TF) inducing effect on monocytes. Small doses of MMA (0.1-1 mg/ml) [corrected] markedly potentiated the TF inducing effect of thrombin or lipopolysaccharide (LPS) which was included as a reference stimulant. These TF modulating effects of MMA were not seen with HUVEC. However, the generation of fibrinopeptide A (FPA) in cell overlay plasma indicated enhanced procoagulant activity of HUVEC treated with moderate doses of MMA, probably reflecting MMA cytotoxicity leading to cell retraction and exposure of extracellular matrix. Furthermore, small doses of MMA had a slight enhancing effect on FPA generation when coincubated with thrombin. These findings indicate that MMA in concentrations found in central venous blood in vivo, alone or together with thrombin, directly or indirectly exert effects that contribute to activation of coagulation.