The effects of moderate 30-min cycle ergometer exercise (aerobic metabolism) followed by short-term exercise at maximal capacity (anaerobic metabolism) on fibrinolytic activity were investigated in ten female and ten male healthy, untrained subjects. The following parameters of fibrinolytic activity were measured initially (t0), at the end of the aerobic phase (t1), at the end of the anaerobic phase (t2) and after a 30-min recovery period (t3): tissue plasminogen activator (PAt) activity, PAt concentration, plasminogen activator (PAt) activity, PAt concentration, plasminogen activator inhibitor (PAi) activity, and D-Dimer concentration. Moderate long-term exercise caused a slight but significant increase in PAt concentration and PAt activity (t1; P < 0.01), whereas short-term exercise at maximal capacity (t2) produced a substantial elevation in both these parameters (P < 0.01). This would suggest that PAt was not inhibited totally by PAi which would itself seem to be consumed during exercise. In addition, a slight exercise intensity-dependent increase in D-Dimer concentration was measured--circumstancial evidence not only for elevated fibrinolytic potential, but also for an actual increase in fibrin degradation (t2: P < 0.01). After t3 both PAt activity and D-Dimer concentration were still slightly but significantly increased. The results obtained in the tests of fibrinolytic activity showed no significant difference between the men and the women. It would seem that the release of PAt is more markedly stimulated by short-term intense physical exercise than by long-term moderate exercise and actually causes increased fibrin degradation.