Our information about gastric pepsinogen secretion and peptic activity is incomplete because of the heterogeneity of pepsinogen and pepsin, and the lack of assays specific for the different pepsins in gastric juice. In general, the peptic activity of gastric juice parallels acid output, and the limited clinical information obtained from tests of gastric acid secretion is not enhanced by the determination of the peptic activity of gastric juice. Nevertheless, the inhibition of this activity is of prime importance in the pharmacotherapy of peptic ulcer disease. This can be accomplished by inhibiting the secretion of acid and pepsinogens, raising the pH of gastric juice, inhibiting the binding of pepsin to its substrate, adsorbing pepsin, or inhibiting the active site of pepsin. The first three strategies have been shown to be effective in accelerating the rate of healing of peptic ulcer.