The present experiment was conducted to quantify the net fluxes of both free and peptide amino acids across the mesenteric and stomach portions of the portal-drained viscera (PDV) of three yak cows (172·3±18·6 kg, BW) fed a straw-concentrate diet at maintenance level. Yaks had been fitted with sampling catheters in the portal vein, mesenteric artery and mesenteric vein prior to its convergence with the gastrosplenic vein. Blood flow was determined by measuring the dilution of para-aminohippurate (PAH) infused constantly into a distal mesenteric vein. Amino acids in the deproteinized plasma were analysed before and after acid hydrolysis. The increased amino acids after acid hydrolysis were considered as peptide-bound amino acids (PAA). The fluxes of free amino acids (FAA) and PAA across PDV and mesenteric-drained viscera (MDV) were calculated as the product of venoarterial differences and plasma flow. Flux across the stomach viscera (SDV) was calculated as the difference between portal and mesenteric fluxes. Portal blood flow was 389 l/h or 2·32 l/h kg BW, of which 37% was contributed by the mesenteric vein. There was net appearance of a large quantity of PAA across PDV, which accounted for 92% of the total nonprotein amino acid flux. Net release of PAA and FAA in SDV accounted for 78% and 42% of the net release in PDV, respectively. These results suggest that in yaks, peptide possibly is the primary form of amino acid absorption, and that the stomach area probably is the major site of peptide absorption.