The pineapple protease, bromelain, selectively inhibits the biosynthesis of proinflammatory prostaglandins, apparently by indirect action.The inhibition of endogenous proteases that accompanies trauma, or prolonged exposure to excessive stress markedly elevates the relative proportions of those prostaglandins responsible for the symptoms of inflammation. It has been demonstrated that bromelain's specificity is similar to that of the endogenous protease plasmin. Bromelain acts on fibrinogen to give products that are similar, at least in effect, to those formed by plasmin. They are small molecular weight active peptides, which regulate prostaglandin biosynthesis and create conditions existing in the healthy organism. It has been shown that a substantial portion of orally administered bromelain is absorbed intact into the bloodstream, thereby elevating the proteolytic and fibrinolytic activity of the blood for hours.The similarity between the beneficial effects of aspirin-type drugs and bromelain, while bromelain causes none of the undesirable side effects of the others, suggests that bromelain acts on the prostaglandin synthetic pathway at a site different from that affected by the non-steroidal anti-inflammatory drugs. While aspirin inhibits the cyclooxygenase and thus the biosynthesis of prostaglandins, it is postulated that bromelain acts further down the arachidonate cascade at the thromboxane synthetase step. Circumstantial evidence suggests that bromelain inhibits the synthesis of the “proinflammatory” prostaglandins without affecting that of the “anti-inflammatory” ones. Bromelain therefore tends to reestablish the balance of the two types of prostaglandins that characterizes the state of the healthy organism.