Clovers (genus: Trifolium) have been used in traditional medicine by many cultures, but the biological activity of the most of these plants still remains unknown. The aim of our in vitro study was to assess the antioxidative action of phenolic extracts from aerial parts of Trifolium scabrum and Trifolium pallidum in human blood plasma, exposed to oxidative stress. In the present study we also demonstrate, for the first time the effects of the tested extracts on coagulative properties and fibrinolytic activity of blood plasma. The protective properties of the examined extracts (0.5-50 μg/ml) against peroxynitrite-induced oxidative stress were estimated by the measurements of 3-nitrotyrosine, thiol groups and the thiobarbituric acid-reactive substances levels. The extracts considerably prevented the oxidative and nitrative damage to plasma proteins. Even the lowest doses of the Trifolium extracts (0.5 μg/ml) were able to markedly reduce 3-nitrotyrosine formation (by about 50%) and to increase the level of -SH groups (by about 30%), in comparison to the plasma exposed to ONOO(-) in the absence of the extracts. The protective action of all the used concentrations of the Trifolium extracts in the prevention of lipid peroxidation was also found. The tested extracts influenced neither the coagulative properties nor fibrinolytic activity of plasma. Moreover, the extracts were able to significantly reduce the inhibitory effect of ONOO(-) on fibrinolytic activity of plasma (assessed with the use of a chromogenic substrate for plasmin).