The influence of the ligands picolinic acid and citric acid on the intestinal absorption of zinc was studied in two different experimental trials with Zn-depleted and Zn-supplied pair-fed rats using everted sacs in vitro and the ligated small intestine in vivo. ZnSO4 was applied in water solution (pH 5.8) without ligands or together with picolinic acid at a molar ratio of 1:0.2, 1:2, and 1:20 or together with citric acid at a molar ratio of 1:1, 1:10, and 1:100. The intestinal Zn transfer of the Zn-depleted rats with picolinic acid is significantly increased only at a molar ratio of 1:20 (zinc:ligand) (P less than 0.001). The other in vitro results of Zn absorption were only slightly improved, mainly at the high molar excess of picolinic acid in comparison to ZnSO4 without ligands. Only a tendency for an increased Zn transfer--however, already at a narrow molar ratio of 1:1 or 1:10--could be seen when citric acid was added. The intestinal uptake was not influenced by citric acid. The absorption of zinc in vivo did not vary in dependence of the addition of picolinic or citric acid in different molar ratio in comparison to ZnSO4 addition without ligands. Zn-depleted rats showed a significantly higher Zn absorption rate than Zn supplied pair-fed rats independently of the kind of ligand and the zinc:ligand ratio (P less than 0.001). These results are discussed in detail.