The effect of adding phytase to the diet on the bioavailability of zinc from organic and inorganic sources was studied in an experiment carried out on 560 broiler chickens aged from 4 to 28 days. Phytase was either added (750 FTU/kg) or not to a low-Zn wheat-soyabean diet. Simultaneously, gradient levels of zinc (0, 10, 20 or 40 mg kg^-1) from fodder ZnSO₄∙H₂O or an organic complex of Zn (Zn chelated with amino acids, ZnAA) were added to the diets without and with phytase. The bioavailability of zinc from ZnAA, calculated using multiple linear regression, was generally higher than from ZnSO₄, especially when the diet was not supplemented with phytase. The relative bioavailability of Zn from ZnAA (Zn from ZnSO₄ - 100%) in phytase-supplemented diets was: 103 (for body weight gain), 104 (for feed conversion), 114 (for Zn content in dried tibiae bones), 114 (for Zn content in tibiae ash), and 109% (for total amount of Zn in tibiae bone). In the diets that were not phytase-supplemented, the corresponding values were: 121, 116, 139, 142 and 117%, respectively.