Objective This study was designed to determine the in vitro effects of different doses and different kinds of Low Molecular Weight Heparin (LMWH) on clot rate (CR), and to determine whether the CR can be used to monitor LMWH. Methods This study was performed in two phases in vitro. The first, CR was measured with different reagent (glass beads, celite and kaolin) on volunteer (n¼20) blood samples spiked with increasing concentrations of LMWH (dalteparin, 0.2e1.8 IU/ml). The second, CR were measured with the same reagent (glass beads) on volunteer (n¼20) blood samples spiked with the same concentrations (0.8 IU/ ml) of different LMWH (dalteparin, enoxaparin and nadroparin). Regression analysis was performed to establish a regression equation from corresponding anti-Xa LMWH levels.