1. The effect of electrical stimulation of the vagus nerve with different patterns of impulses (the total number of stimuli remaining constant) on gastric acid secretion and gastric motility were investigated in the anaesthetized ferret. Three stimulus patterns were used: continuous, bursts at ten times the continuous frequency but for a tenth of the time, and a natural burst pattern obtained from a recording of vagal efferent fibre discharge. 2. The natural burst pattern gave rise to gastric contractions of larger amplitude than either the artificial burst or continuous stimulation, while continuous stimulation gave rise to larger changes in tonus. Acid secretion, however, was reduced by the natural pattern of stimulation as compared to the output during continuous stimulation, but to a lesser extent than that due to artificial burst stimulation. 3. Burst stimulation at 10 impulses/sec resulted in a larger output of acid and greater amplitude of gastric contraction than the equivalent continuous stimulation. This potentiation was lost at stimulation frequencies above 30 impulses/sec. 4. At burst frequencies of 60 and 120 impulses/sec there was a marked reduction in acid output and amplitude of contraction as compared with continuous stimulation at 6 and 12 impulses/sec respectively. 5. These results are discussed in relation to the functional significance of the different patterns of vagal discharge seen in the anaesthetized ferret.