Abstract Nineteen healthy young men were subjected randomly to maximal exercise on treadmill, venous occlusion (VO) and infusion of DDAVP on three different mornings. Alter exercise t-PA antigen increased by 2.8 fold, after VO by 5.1 fold and after DDAVP by 2.4 fold (all P<0.01). PAI-1 antigen did not change significantly after any of the stimuli. Therefore, increases in t-PA activity and decreases in PAI-1 activity observed after stimulation were attributed to released t-PA antigen only: increase in t-PA activity after exercise was 2.2 fold lower than that after VO and 1.8 fold higher than after DDAVP. No PAI-1 activity could be detected in 81 9 samples after exercise, in 15 19 samples after VO and in 5/19 after DDAVP. Positive correlations were observed for t-PA antigen release between the three stimuli (VO-DDAVP: r=0.78, P<0.01; exercise-DDAVP: r=0.53, P<0.05; VO-exercise: r=0.30, not significant). It was concluded that maximal exercise as a stimulus of t-PA release is less effective than VO and similar to DDAVP. Divergent alterations of t-PA and PAI-1 antigens after stimulation argue against a common regulation of their acute release from tissue stores.