The physiological mechanism of exercise-induced hyperfibrinolysis is not fully understood. It has been reported that exercise increases plasma arginine vasopressin (PAVP) and that PAVP infusion enhances blood fibrinolytic activity (FA). To characterize the fibrinolytic role of PAVP during exercise, PAVP and FA were examined before and after submaximal and maximal exercise in 16 normal, healthy volunteers. After completion of a 100% VO2max exercise test on a bicycle ergometer, which elicited exhaustion in 14.3 +/- 1.4 min (MSD), subjects were randomly assigned to exercise trials at 40% and 70% VO2max for 15 min, each of the three tests being separated by 7 d. Prior to and immediately after the completion of the respective exercise treatment, heart rate, VO2 uptake, and respiratory quotient were measured and venous blood was removed and analyzed for PAVP using radioimmunoassay. The fibrin plate method (FP) and euglobulin lysis time (ELT) technique were employed to assess FA. The intrinsic and extrinsic plasminogen activators' response to all exercise treatments was also examined in pooled plasma prepared from the same subjects. Differentiation between the intrinsic and extrinsic activators' activity was ascertained in the FP by blocking the former with the addition of C1-inactivator. Lactic acid was measured using a standard spectrophotometric method. Compared to rest, FA was significantly increased (P less than 0.05) in all exercise tests when assessed using ELT, with a response related to exercise intensity. However, the 40% VO2max exercise trial caused a nonsignificant increase (P greater than 0.05) in FA using the FP method, with a significant increase (P less than 0.05) being observed in 70% and 100% VO2max exercise tests.(ABSTRACT TRUNCATED AT 250 WORDS)