There is much interest in in vitro thrombosis systems using exclusively human materials for evaluating new drugs. We have previously developed such a model using a perfusion chamber in which whole blood anticoagulated with low-molecular-weight heparin (LMWH) was circulated over the extracellular matrix of endothelial cells that had been stimulated with phorbol myristate acetate to cause tissue factor formation. Here we studied various LMWHs and a pentasaccharide to find out which was most useful in an in vitro thrombosis model. We compared unfractionated heparin, two commercial LMWHs (Fragmin and Fraxiparine), one commercial heparinoid (Orgaran), and a chemically synthesized derivative of the natural pentasaccharide (Org 31550). Blood was anticoagulated with the concentration of each glycosaminoglycan that prevented thrombin formation for at least 3 hours in the test tube (Fragmin, 20 anti-Xa U/mL; Fraxiparine, 40 anti-Xa Institute Choay U/mL; Orgaran, 15 anti-Xa U/mL; Org 31550, 200 anti-Xa U/mL; unfractionated heparin, 5 IU/mL) and recirculated over the matrix of unstimulated cells (no tissue factor in the matrix) and phorbol-stimulated endothelial cells (tissue factor in the matrix). Platelet adhesion, aggregate formation, and fibrin deposition were evaluated. In perfusions over the extracellular matrix of unstimulated cells, the highest platelet adhesion rates were observed with Orgaran. Fibrin deposition was absent with unfractionated heparin in phorbol-stimulated matrix. Increasing amounts of fibrin were observed with Orgaran, Fragmin, and Fraxiparine. Most fibrin was found with the pentasaccharide Org 31550.(ABSTRACT TRUNCATED AT 250 WORDS)