Seven days of dosing with either 30 mg or 60 mg of lansoprazole were compared with placebo in a double-blind, randomized, three-way cross-over study in 12 male healthy volunteers. Twenty-four-hour intragastric pH was measured after 7 days of dosing with each regimen, as well as 3 and 7 days after the end of dosing. During dosing with placebo, intragastric pH was above 4 for a median of 51 minutes. pH values were significantly raised to above 4 for 8.45 and 8.33 hours on Day 7 of dosing with lansoprazole 30 and 60 mg, respectively, but returned to normal by the third day after stopping dosing. No clinically relevant influence on endocrine function (serum concentrations of insulin, aldosterone, testosterone, parathormone, glucagon, T3, T4, TSH, LH, FSH, STH, prolactin, circadian cortisol profile, ACTH test) was observed. No serious adverse clinical or laboratory events were noted.