BACKGROUND: Hemodilution reduces the concentration of clotting factors in blood and it may induce some degree of coagulation impairment. The goal of this study is to investigate the changes of coagulation status during progressive hemodilution with several solutions. METHODS: Sixty healthy patients were randomly allocated to six groups according to experimental solution, and each group contained 10 patients. Whole blood was diluted by 0%, 10%, 25%, 50% with 0.9% normal saline, 4% modified fluid gelatin, 10% pentastarch, 10% dextran 40 and two brands of 6% hydroxyethyl starchs (Salinehes(R) , HAES-steril(R) ). At each dilution, thromboelastographic parameters {(r, k, alpha angle, maximum amplitude (MA)} were measured using thromboelastography (TEG) and were compared with those of an undiluted specimen obtained concurrently from the same patients. RESULTS: Hemodilutions of 25% and 50% with 0.9% normal saline decreased r and k times, and increased alpha angle but there was no difference in MA. Hemodilutions of 10% and 25% with modified gelatin solution did not change the parameters. However, 50% hemodilution of the gelatin solution decreased the k time and increased alpha angle. Hemodilutions of more than 10% with 10% pentastarch increased the k time, decreased alpha angle and MA. Hemodilutions of more than 10% with 10% dextran 40 increased r and k times, and decreased alpha angles and MA according to the quantities of this dilutional solution. Hemodilutions of more than 25% with 10% dextran 40 increased k times above 400%. Hemodilutions of more than 10% of 6% HES (Salinehes(R) , M.W: 70,000 dalton) decreased MA. Hemodilutions of more than 10% of 6% HES (HAES-steril(R) , M.W: 200,000 dalton) decreased the alpha angle. CONCLUSIONS: 25% and 50% hemodilutions of 0.9% normal saline induce a hypercoagulable state, but hemodilutions of more than 10% with each colloid solution decreased coagulability of whole blood according to the degree of dilution, except in the case of modified fluid gelatin solution. Hemodilutions of more than 25% with 10% dextran 40 induce a severe coagulation impairment.