In normal subjects, the gastric ionisation of calcium and phosphate seems to be a prerequisite for their intestinal absorption. We investigated the behavior of the plasma calcium and phosphate profile in 30 patients on regular dialysis treatment in the 6 h following a meal containing 1 g of calcium and 2 g of phosphate. Moreover, to assess the role of gastric acidity, the study was repeated after 3 days on omeprazole administration, to nearly abolish gastric acid secretion. Both total plasma calcium and ionized calcium peaked after the meal (at 30 and 120 min, respectively) only in basal study, while no peak was observed after the administration of omeprazole. Surprisingly, both in basal and in the omeprazole study the levels of plasma phosphate did not increase after the test meal. In conclusion, as in normal subjects, the gastric ionization of dietary calcium promotes the intestinal absorption of calcium in uremic patients on dialysis treatment, while the acute gastric acid inhibition by omeprazole reduced the intestinal calcium transport. In contrast, with the ‘trade off’ hypothesis we did not observe any postprandial phosphate peak after the dietary load, and, in contrast with normal subjects, omeprazole administration did not influence the phosphate profile.