We studied the effects of hypertonic (7.5%) and normal saline on coagulation and fibrinolysis in an in vitro model using thromboelastography of human whole blood. Reaction times increased and alpha angles decreased with hypertonic saline replacement at 7.5% blood volume compared with similar dilution with normal saline. At 10% blood volume replacement with hypertonic saline, reaction and coagulation times were significantly increased and alpha angles were decreased. Clot lysis at 30 min was also significantly reduced. We conclude that 7.5% hypertonic saline solution has anticoagulant effects if it replaces 7.5% or more of blood volume.