Technical Abstract: Methionine (Met) is an indispensable sulfur amino acid that functions as a key precursor for the synthesis of homocysteine and cysteine, via transmethylation (TM) and transsulfuration (TS), respectively. We previously showed that significant catabolism of indispensable amino acids, such as lysine and leucine, occurs in the gut. Our aim was to quantify the extent of gastrointestinal first-pass methionine metabolism in piglets. Four-week-old, formulafed piglets (n=16) were given an intraduodenal (ID) and intravenous (IV) infusion of [1-13C]-[2H3]methionine on two separate days in a cross-over design. Arterial isotopic enrichments of methionine, homocysteine, and CO2 were measured by GC/IR-MS and whole body fluxes are expressed as µ mol x kg-1 x h-1. Methionine flux did not differ between the IV and ID group (171 vs 170). Methionine metabolism via TM to homocysteine accounted for ~30% of the methionine flux and was not different between the IV and ID group (46 vs 51). Methionine TS estimated from conversion of 13C-Met to 13CO2 also did not differ between IV and ID, representing ~20% of Met flux (34 vs 32). In contrast, remethylation of homocysteine to methionine was higher (p<.01) in ID than IV (18 vs 11). We conclude that first-pass dietary methionine metabolismvia TM and TS is limited in enterally-fed piglets. Research support: USDA.