Ulcers were produced in the gastric mucosa in rats. After 90 days of healing, one group of animals was given pentagastrin and carbacholine via continuous subcutaneous infusion. After 1 h the animals were killed and the wounds and normal mucosa beside the wounds were prepared for electron microscopy. Stereological analyses of regenerating parietal cells from the wounds revealed that stimulation by the secretagogues increased the secretory surface density by some 76%. pH studies were performed in the wounds in another group of animals after the same stimulation as above, and it was found that the secretory product was acid. Thus, immature parietal cells in healing gastric wounds reacted normally to the secretagogues given and they were able to secrete HCl.