The influence of acute bouts of dynamic exercise on plasma tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI) and fibrinogen was investigated on nine healthy non-smoking men aged 23 to 37 years. Subjects performed maximal and two submaximal (duration 30 min, intensity 50% [aerobic threshold] and 78% [anaerobic threshold]VO2max) bicycle ergospirometry tests separated by seven days. The order of the submaximal tests was randomized. Blood samples were drawn before, immediately after and 24 h after each test. Plasma tPA and PAI activities were measured amidolytically, and fibrinogen concentration by thrombin method. All postexercise values were corrected for the change in plasma volume. The pre-exercise tPA and PAI activities and fibrinogen concentration were similar in each tests. tPA activity increased during each test (from 2.0 [SEM 0.24] IU/ml to 20.3 [3.14] during maximal, 2.0 [0.22] to 19.0 [2.59] during anaerobic threshold test, 1.8 [0.22] to 5.5 [0.82] during aerobic threshold; p < 0.001 during all tests, p = 0.01 aerobic threshold vs maximal and anaerobic threshold). PAI activity decreased during maximal (from 6.6 [2.51] AU/ml to 2.0 [2.00], p < 0.05) and anaerobic threshold (5.0 [2.07] to 0.2 [0.22], p < 0.01) tests but not during aerobic threshold test (7.0 [3.69] to 4.5 [2.93], p = 0.123). One subject had clearly higher pre-exercise PAI activity and smaller tPA response to exercise as compared to other subjects. All 24 h post-exercise activities were similar to pre-exercise values. Plasma fibrinogen concentration did not change during any tests.(ABSTRACT TRUNCATED AT 250 WORDS)