The initiation of the angiogenic process requires a locally confined and time‐limited proteolysis of the basement membrane (BM) components at the site of new vessel sprout. Gelatinase A, a member of the matrix metalloproteinase family, degrades BM type IV collagen and is involved in the BM breakdown by migrating tumor cells and endothelial cells (EC). Gelatinase A is synthesized as latent proenzyme and must be activated in order to express its proteolytic activity. A plasma membrane‐dependent mechanism of activation has been described for several tumor and transformed cell lines. In the present study, we show that latent (72 kD) and mature (62‐59 kD) froms of gelatinase A are present in EC membrane fraction from Triton X‐114 extract while only latent form is found in the cytosolic fraction. The incubation of EC membrane fraction with exogenous latent gelatinase A resulted in a significant activation giving rise to 62–59 kD mature forms. 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), a strong potentiator of angiogenesis in vitro and in vivo, increases the amount of both latent and activated forms of gelatinase A in EC membrane fraction as well as the ability of this latter fraction to activate exogenous latent gelatinase A. We show that the mRNA transcript coding for the membrane‐integrated MMP, the MT‐MMP, previously described as a potential gelatinase A activator in invasive tumor cells is also expressed in vascular EC and is regulated through a TPA sensitive process. This enzyme may be responsible for membrane‐dependent gelatinase A activation in normal vascular EC and may therefore be a determinant in the control of BM proteolysis during angiogenesis. © 1995 Wiley‐Liss Inc.