Clot retraction and fibrinolysis may present as a decrease in amplitude on thrombelastography (TEG). The former represents normal or hyperactive platelet function, and the latter represents a fibrinolytic state. It is important to distinguish clot retraction from fibrinolysis because the treatment of each condition is different. To distinguish between these phenomena, we performed TEG with platelet-poor plasma (PPP) and platelet-rich plasma (PRP) with an increasing platelet count (range, 50-1200 x 10(9)/L) with or without abciximab. Maximum amplitude (MA) and the percentage decrease of amplitude at 30 and 60 min after MA were examined for each sample. Blood samples to which tissue plasminogen activator (tPA) was added served as positive controls for fibrinolysis. Morphological changes of clots and D-dimer levels were also examined. With higher platelet counts, the percentage decrease of amplitude after MA increased significantly at 30 and 60 min, but not in the abciximab samples. Morphological changes of clots have shown clot retraction in PRP, but not in PPP or PRP pretreated with abciximab. D-dimer levels increased only in samples to which tPA was added, but not in native PPP or PRP samples. In conclusion, we have shown that the decrease in amplitude at 30 and 60 min can be due to platelet-mediated clot retraction and can be attenuated by sample pretreatment with abciximab, which interrupts platelet-fibrin(ogen) binding.