Time-response and dose-response curves for acid output to continuous infusion of histamine (HIST) and pentagastrin (PG) were determined by two techniques in conscious rats provided with chronic gastric fistula. With the step-dose technique the dose of the stimulant was increased each hour; with the single-dose technique only one dose of the stimulant was administered on each test day. The observed maximum acid output (OMAO) was obtained either by infusion of PG at a rate of 6 μg/kg/h using both techniques or HIST at a rate of 1 mg/kg/h with the single-dose and 2 mg/kg/h with the step-dose technique. These OMAO were in the order: single PG > single HIST > step HIST > step PG in ratios 100 – 99 – 83 – 82. The dose-response curves were also analyzed by application of the Michaelis-Menten equation. For each stimulant there was no difference between the calculated maximum acid output (CMAO) whatever the technique used, but PG gave lower CMAO than HIST (p < 0.05). For both stimulants the calculated doses for half the calculated maximal response (CD 50) are significantly higher with the step-dose than with the single-dose technique. These results are compared with those previously described in the literature for cats, dogs a