Objective: To study the role of alpha(2)-antiplasmin (alpha(2)-AP), the main physiological plasmin inhibitor, in controlling vascular and cellular proteolytic activity. Materials: Arteries, organs and cell cultures derived from alpha(2)-AP-deficient (alpha(2)-AP(-/-)) mice or from their wild-type littermates (alpha(2)-AP(+/+)). Results: In serum-free conditioned medium of alpha(2)-AP(+/+) or alpha(2)-AP(-/-) skin fibroblasts, the time course (0-72 h) of PAI-1 antigen and of t-PA or u-PA antigen and activity production was similar. Activation of proMMP-9 (gelatinase B) upon addition of plasmin(ogen) to serum-free conditioned medium of fibroblasts was consistently detectable with alpha(2)-AP(-/-) but not with alpha(2)-AP(+/+) cells. In aorta and femoral arterial extracts of alpha(2)-AP(+/+) or alpha(2)-AP(-/-) mice, t-PA and u-PA activity levels were comparable, and fibrin zymography with cryosections did not reveal significant differences in fibrinolytic activity. In liver or kidney extracts of alpha(2)-AP(+/+) or alpha(2)-AP(-/-) mice, t-PA, u-PA, PAI-1 and plasminogen antigen levels were comparable; t-PA or u-PA activity was not detected in liver extracts and was present at comparable levels in kidney extracts. Activation of plasminogen to plasmin in solution by cell-associated plasminogen activator, and activation of cell-bound plasminogen by tcu-PA was comparable for fibroblasts of both genotypes. Conclusions: alpha(2)-AP does not play a crucial role in controlling vascular or cellular proteolytic activity in mice. (C) 2000 Harcourt Publishers Ltd.