The dose-response relationship of oral famotidine at doses up to 10 mg was evaluated in 10 healthy male subjects to assess the extent and duration of inhibition of meal-stimulated intragastric acid secretion. Each subject received single oral administrations of famotidine 0.5, 2.5, 5.0, and 10.0 mg and placebo in a double-blind, randomized, cross-over fashion. Intragastric pH was measured every 4 seconds for 24 hours and expressed as the mean pH for each 10-minute interval. Standard high-protein meals were provided 1 hour before each dose of study drug and at 3 and 9 hours postdose. The mean intragastric pH was significantly higher after famotidine doses 2.5, 5.0, and 10.0 mg than after placebo at times 2.5 to 3.0, 1.8 to 3.2, and 1.7 to 4.2 hours postdose, respectively. There were no significant differences in mean pH seen between famotidine 0.5 mg versus placebo. The range of the pH means between 1.7 and 3.2 hours postdose was placebo (1.0 to 1.3), famotidine 0.5 mg (1.1 to 1.4), 2.5 mg (1.4 to 1.7), 5.0 mg (1.7 to 2.1), and 10.0 mg (2.0 to 2.3). There was a statistically significant linear dose-response relationship between famotidine dose and intragastric pH between 1.7 and 3.8 hours and from 6.3 to 8.7 hours after ingestion.