The pharmacokinetics of orally administered mefloquine were determined in six healthy male subjects and in six ulcer patients before and after a 3-day course of cimetidine (400 mg morning and evening). Peak plasma concentrations Cmax and AUC0−∞ were similarly and significantly (P<0.05) increased after cimetidine pretreatement in both healthy subjects and peptic ulcer patients Cmax was increased by 42.4% and 20.5% while AUC0−∞ was increased by 37.5% in healthy and peptic ulcer subjects respectively. The values of t1/2ab absorption and t1/2β elimination, totall crearance CLT/F and volume of distribution were altered to varying levels after cimetidine treatment but the changes were not statistically significant in both healthy and peptic ulcer subjects.