To study the stomach role in exogenous oxalate absorption. The kinetic variation of urinary oxalate excretion (mg/min) in 10 healthy adults and 8 patients who underwent total gastrectomy was investigated before and after an oral spinach oxalate load. The bioavailability of the oxalate load in the healthy adults was calculated and compared with that in the patients. The oxalate content in the oral spinach load was 2567-2670 mg. The urinary oxalate excretion (mg/min) in the 10 healthy adults increased significantly 20 minutes after loading (this increase was compared against their basic oxalate excretion level of 0.0331 +/- 0.0203). Further observations after loading include: a first peak of oxalate excretion 40 minutes after loading; an oxalate excretion level double that of the basic level after 60 minutes (0.0732 +/- 0.0294) and a second peak appearing at 3 hours (P < 0.01). A "first peak" (0.063% +/- 0.062%) was not in any of the patients who underwent a total gastrectomy. Furthermore, a bioavailability of oxalate, which was 50% lower than that in the healthy subjects, appeared 60 minutes after loading (0.098% +/- 0.071%, P < 0.01). The stomach is a powerful oxalate absorption organ under normal physiological conditions. Further investigation on the relationship between stomach dysfunction and urinary calcium oxalate formation is needed.