Twelve healthy male volunteers participated in a randomized placebo-controlled, three-period cross-over study to assess the effect of a new effervescent citrate-cimetidine combination (200 mg cimetidine/tablet) (C) on intragastric pH in comparison with a liquid aluminium-magnesium hydroxide antacid (A) and placebo (P). The intragastric pH values were determined by an Ingold combined glass electrode and recorded by a "pH 60" portable unit. Each pH-metry lasted 5 hours and was performed on three separate occasions at one-week intervals. Each treatment was orally administrated at 09.00 h, following a 1-hour baseline intragastric pH recording. The effect of C was measurable almost immediately after drug intake with a median pH between 5-6.5 within 3 minutes, lasting for a mean of 110 minutes and median pH greater than 4 for at least 4 hours. The rise of gastric pH with C was higher (P less than 0.01) and longer (P less than 0.01) than that of A: median pH between 3.5 and 4.5 for 10 to 35 minutes, pH above the placebo curve for 140 minutes and above pH 3 for 50 minutes. In terms of percentage of time at or above each pH level, the differences between the three treatment groups were significantly in favor of C compared to A and A compared to P.