The present study investigated the effects of adding a multicarbohydrase enzyme (MC; 4000 units/g xylanase, 1000 units/g α-amylase, 500 units/g protease, 150 units/g β-glucanase) to a high-fiber diet on net portal fluxes of essential AA (EAA) and urea-N in growing pigs. Five female pigs (22.8 ± 1.6 kg BW), with permanent catheters in the portal vein, ileal vein and carotid artery, were fed 3 isocaloric/nitrogenous diets at 4% of their BW once daily at 0900 h for 7 d in a replicated 3 × 3 Latin square design. The diets contained corn and soybean meal with 0% (CTRL) or 30% distillers dried grains with solubles (DDGS; HF) produced from a 1:1 mixture of wheat and corn. The third diet was supplemented with MC in addition to the 30% DDGS (HF+MC). On d 7, para-amino hippuric acid was infused into the ileal vein (to measure flow rate) and blood was sampled from the portal vein and carotid artery for 7 h after feeding to assay EAA and urea-N. Portal absorption of nutrients was derived by multiplying the porto-arterial plasma concentration differences by portal vein plasma flow. Diet had no effect (P > 0.10) on postprandial portal vein plasma flow rate and net urea-N flux, but portal urea-N was lower (P < 0.05) during the first h and tended to be lower (P = 0.07) over the 7 h in pigs fed CTRL. Postprandial portal Arg, Ile, Leu, Trp, and Val were lower (P < 0.05) in HF-fed pigs from 30 to 240 min than CTRL-fed pigs and MC supplementation tended (P < 0.10) to or improved (P < 0.05) portal fluxes of those AA. Further, pigs fed CTRL had higher (P < 0.05) net portal fluxes of the above-mentioned AA from 30 to 120 min postprandial. Also, CTRL-fed pigs had higher (P < 0.05) net portal fluxes of most EAA and pigs fed HF+MC had higher (P < 0.05) Lys and similar Met and Phe (P > 0.10) net portal fluxes compared with CTRL-fed pigs. The results showed that supplementing the HF diet with MC improved net portal appearance and fluxes of some EAA in growing pigs.