In an attempt to control gastric acid secretion with operant-conditioning techniques, four normal women were given visual feedback on gastric pH plus money reinforcers.When money was made dependent on increased secretion in a differential-reinforcementof-high-rates schedule, the rate of secretion of three of the four subjects increased to three times baseline. When money was then made dependent on decreased secretion in a differential-reinforcement-of-other-behaviors schedule, the rate of secretion of these three subjects returned to baseline levels. Heart rate, respiratory frequency, abdominal electromyographic activity, and stomach motility (measured by the electrogastrogram method) were not consistently correlated with acid secretion across subjects, although individual subjects showed substantial correlations between acid secretion and one or more other physiological response.DESCRIPTORS: gastric acid secretion, operant conditioning of gastric acid secretion, gastric pH, biofeedback, differential reinforcement of high rate to increase gastric acid secretion, DRO to reduce gastric acid secretion, visceral learning A variety of autonomic responses have been modified with operant-conditioning procedures (Miller, 1969;Shapiro and Schwartz, 1972). Miller (1969) and others have called attention to the possible value of these techniques in the treatment of psychophysiologic disorders. Successful clinical applications have included elimination of ruminative vomiting (Lang and Melamed, 1969), reduction in cardiac arrhythmias (Weiss and Engel, 1971), and reduction of blood pressure in essential hypertension (