Thrombin generation, as evidenced by plasma fibrinopeptide A (FPA) concentrations, was studied during blood collection from donors taking oral contraceptives (OC). 450 ml blood were drawn into Fenwal PVC bags from 26 OC users and 28 nonusers. Blood samples for determination of FPA, beta-thromboglobulin (BTG), thrombotest (TT), prekallikrein (PKK), antithrombin-III (AT-III) and factor VIII procoagulant activity (FVIII:C) were drawn from the bags immediately after ending blood donation and following storage for 24 h at 4°C. The FPA concentrations following donation were significantly higher in the OC than in the control group (p<0.05). The levels of PKK were also higher in blood obtained from OC users (p<0.001), as was the FVIII:C level, the latter difference, however, was not significant (p=0.06). No cold-promoted activation of factor VII, as evidenced from TT, was detected following storage at 4°C, neither was any change observed in the FPA, PKK and AT-III levels. The BTG concentrations increased significantly during storage, most pronounced in the control group (p<0.05). The decay of FVIIIiC was similar in the two groups, averaging 24.7%. No correlation was observed between the FPA levels and the other parameters determined. We conclude that thrombin generation is more pronounced during routine blood collection from donors taking OC.