Compared to modern breeds, Iberian pigs have lower rates of muscle protein deposition and greater viscera weight. Factors that limit growth performance of Iberian pigs are unknown. We hypothesized that differences in net portal appearance of the essential AA Lys and Met might partially explain the lower growth rate reported in Iberian pigs compared to modern breeds. Net portal appearance of AA was measured in 6 Iberian and 6 Landrace gilts (28 kg BW) fitted with chronic catheters in the portal vein, carotid artery, and mesenteric vein. Blood samples were taken for 6 h after feeding 2 isoenergetic diets (14.0 to 14.5 MJ ME/kg DM) with low CP (LCP) and high CP (HCP) (13 vs. 16%, respectively) in a crossover design after a 1-wk adaptation. Net portal appearance of Lys was greater (P < 0.05) when pigs consumed the HCP than LCP diet (23 vs. 15 μmol/min); breeds did not differ. Net portal appearance of Met tended to be higher (P = 0.076) for pigs fed HCP than LCP diet (4.4 vs. 3.6 μmol/min); breeds did not differ. In conclusion, differences in portal appearance of Lys and Met did not exist between Iberian and Landrace pigs fed barley (Hordeum vulgare)-soybean (Glycine max) diets with low and high protein concentration.