Proteolytic damage is a late event in the molecular cascade initiated by brain injury. Earlier, we proposed that matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA) are important in secondary brain injury. We have shown that intracerebral injection of activated 72-kDa type IV collagenase (gelatinase A) opens the blood-brain barrier, and that during hemorrhagic brain injury there is endogenous production of 92-kDa type IV collagenase (gelatinase B) and uPA. Therefore, to study the functional link between proteolytic enzymes and blood-brain barrier damage, we induced MMP expression by infusing tumor necrosis factor-alpha (TNF) intracerebrally in rats. Initially, the effect on capillary permeability of increasing doses of TNF, using [14C]sucrose uptake, was measured. Then, the time-course of the capillary permeability change was studied at 4, 16, 24 and 72 h. Expression of MMP and uPA was measured by zymography at 24 h after TNF injection and compared to saline-injected controls. A dose-dependent increase in capillary permeability was seen 24 h after TNF injection. Maximal uptake of [14C]sucrose occurred at 24 h compared to saline-injected controls (P < 0.05). Zymography showed production of gelatinase B, which was significantly greater than in saline-injected controls at 24 h (P < 0.05). Batimastat, a synthetic inhibitor to metalloproteinases, reduced sucrose uptake at 24 h (P < 0.0001), and was effective even when given 6 h after TNF (P < 0.01). Thus, gelatinase B is the intermediate substance linking TNF to modulation of capillary permeability. Agents that interfere with transcription of proteolytic enzymes or block their action may reduce delayed capillary injury, extending the therapeutic window.