Because the rat model of biotin deficiency and biotin metabolism has important limitations, we sought to determine whether the urinary profile of biotin and its metabolites in pigs is similar to that in humans. Biotin labeled with either 3H on the side chain or 14C on the ureido ring was administered intravenously to 2-mo-old male pigs. Biotin and its metabolites were identified and quantified by HPLC and radiometric flow detection. At tracer doses of [3H]biotin, 12 +/- 6% (mean +/- SD, n = 3) of total administered radioactivity was excreted within 72 h; at a physiologic dose of [14C]biotin, 47 +/- 2% (n = 5) of the administered radioactivity was excreted within 72 h. Biotin was the major form excreted, as it was in humans. Substantial amounts of bisnorbiotin and biotin sulfoxide, two known biotin metabolites, were also excreted. Bisnorbiotin methyl ketone and biotin sulfone, two biotin metabolites recently identified in human urine, were also present in pig urine. This study provides evidence that biotin metabolism in pigs resembles that in humans.