The thrombin potential (TP) has been defined as the time integral of (i.e. the area under) the thrombin generation curve. It has been shown that this parameter decreases with all types of anticoagulant treatment and increases with ATIII deficiency. We evaluated the use of this parameter for detection of the hypercoagulative state known to accompany oral contraception. In fresh frozen control plasma the TP could be determined with high reproducibility (n = 82, c.v. 2.9%). The TP was linearly diminished by mixing fresh frozen plasma with prothrombin deficient plasma while a high coefficient of correlation was observed (r = 0.997). Women using oral contraceptives showed a significantly (p <0.0001) higher TP (TP = 569 nM·min, SD = 55, n = 17), compared to men or, to women not using oral contraceptives (TP = 484 nM·min, SD = 52, n = 41). This suggests that the thrombin potential indicates the prethrombotic state known to exist in women using oral contraceptives.