1. A new preparation of gastric mucosa isolated from new-born piglets is described. The piglet gastric mucosa was easily separated from the serosal muscle layers by a "blistering" technique which appeared to cause minimal trauma to the tissue and which allowed extended study in vitro in a suitable chamber. Normal resting p.d. was approximately minus 30 mV (mucosal side negative with respect to serosal side), resistance about 100 omega. cm-2 and H+ secretion was absent or occurred at very low rates (0-1mu-equiv/cm-2. hr). 2. Maximally stimulating doses of histamine (1-6 times 10-5 M) caused H+ secretion to increase (up to 15 muequiv/cm-2. hr), p.d. to increase and resistance to decrease. A close correlation was observed between the increase in H+ secretion and decrease in transmucosal resistance. The threshold dose of histamine appeared to be 10-8 M; concentrations 10-4 M and higher reduced H+ secretion somewhat. 3. Pentagastrin ( 10-9-10-7 M) and acetylcholine (10-7-10-5 M) did not significantly stimulate the piglet gastric mucosa. Pentagastrin concentrations above 4 times 10-6 M reversibly inhibited H+ secretion of histamine-stimulated mucosa. High concentrations of acetylcholine (above 4 times 10-4 M) did not affect histamine-stimulated H+ secretion, but a significant reduction in p.d. was observed. 4. This investigation demonstrates the utility of the piglet gastric mucosa for in vitro studies of the mechanism H+ secretion and the action of secretagogues. From a consideration of such factors as the thinness of tissue and ease of preparation it is suggested that neonatal animals may represent a good source of in vitro mammalian gastric tissue.