The apparent widespread extent of zinc (Zn) deficiency in developing countries and the efficacy of oral Zn supplements as an adjunct to oral rehydration therapy make oral Zn supplementation an increasingly important modality in clinical medicine and public health. In this study we aimed to compare the relative bioavailability of oral doses of 30 mg of Zn in two dosing forms.In total, 10 healthy male volunteers ingested oral Zn doses with 200 ml plain water at about 0830 hours in the fasting state on two occasions, once as 30 mg of Zn in an aqueous solution of reagent grade zinc sulfate (ZnSO(4)) and another time as 1.5 NutriSet Zn tablets (Nutriset, Malaunay, France); on a third occasion, only plain water was consumed. Venous blood specimens were collected at baseline, 60, 120, 180 and 240 min after ingestion and the plasma Zn was measured for each sample. The relative bioavailability of oral Zn from a commonly used, tableted (NutriSet) form is only about half of that of a reference dose of aqueous ZnSO(4) as indicated by the area under the curve of serial plasma Zn excursion and maximal change in circulating Zn. Reduced or absent functional outcomes in Zn intervention trials may derive, in part, from a lower than anticipated intestinal uptake of the Zn in the tableted form.