The hemostatic parameters, particularly with respect to F.XIII subunits, were examined in 48 untreated UC patients (22 at active and 26 at quiescent stage). UC active patients showed a significant decrease of F.XIII subunit "a," compared with healthy subjects, as well as in UC patients in remission. In contrast, the level of F.XIII subunit "b" in each group was similar. Compared with normal subjects, UC active patients revealed a significant decrease in AT III concentration, prolonged ELT, and elevated fibrinogen level. In addition, the elevated titer of SDPS test for SFMC appeared in approximately 40% of those patients. However, no strict relationship was found between the presence of positive SDPS and diminution of AT III, as well as of F.XIIII subunit "a" in active UC state. In patients in remission, AT III level and ELT were similar to those as in the control group, but fibrinogen concentration was elevated. Such constellation of hemostatic parameters may indicate a tendency to blood hypercoagulability in UC active patients, whereas, in general, these changes are not associated with the stage of remission. The present data may also suggest that F.XIII behavior pattern should be taken into account in the clinical management of UC.