The purpose of the present work was to compare the bioavailability of structural fluorine contained in sepiolite and in sodium fluoride for laying hens. Three hundred 27-wk-old laying hens were fed one of three diets: 1) a control based on corn, barley, and soybean meal containing 21 mg/kg of fluorine; 2) a sepiolite diet in which 2% sepiolite replaced 2% barley in the control diet and which contained 217 mg/kg of fluorine; and 3) a NaF diet, consisting of the same control diet to which NaF was added to contain 217 mg/kg of fluorine (the same level of F- as the sepiolite diet). The experiment ended when hens were 64 wk old. Fluorine concentration in the tibial bone of hens fed the NaF diet was four times higher than in the control, and twice as high in eggshell. In contrast, hens fed sepiolite had fluorine concentrations in tibial bone and eggshell not significantly higher than fluorine concentrations in the controls. These results indicate that fluorine from sepiolite was not available. The effects of the different diets on egg production, feed intake, feed conversion, egg weight, shell and interior egg quality, dry matter of feces, and body weight gain were also determined but no significant differences due to the dietary treatment were observed.