The dose-response (DR) curves for acid output to intravenous pentagastrin were determined by two techniques in conscious rats with chronic gastric fistula. With the continuous DR technique, the dose of pentagastrin was doubled each hour; with the single DR technique, one dose of pentagastrin was infused for 5 h on each test day. The acid response to all doses but the lowest were higher with the single DR than the continuous DR technique, but the dose required to produce half the maximal response did not differ with the two techniques. Similar results were obtained when the DR curves were analyzed by application of the Michaelis-Menten equation. Accordingly, in conscious rats with gastric fistulas, the single DR technique gives a higher figure for the secretory capacity of the parietal cells than the continuous DR technique, but the two techniques give the same estimation of the sensitivity of the parietal cells.