Heat stress (HS) appears to increase intestinal cell death in pigs, which in turn may increase endogenous intestinal losses (EIL) of proteins and amino acids (AA). Experimental objectives were to analyze the effect of HS on the AA composition of intestinal endogenous proteins and the EIL of AA in pigs. Eight pigs (24 kg initial BW) were surgically implanted with T-type cannulas at the end of the small intestine. After surgery recovery, all pigs were adapted to a protein-AA-free diet and trained to consume the same amount of feed twice a day for 7d in thermo-neutral (TN) conditions (22 ± 2°C). On d 8 of TN conditions ileal content was collected during 12 consecutive h. On d 9 pigs were exposed to natural HS conditions (31 to 37°C) for 8 d. During the HS period ileal content was collected again on d2 (HSd2) and d8 (HSd8). Chromic oxide was used as indicator of the intestinal digesta flow. Data were analyzed using PROC MIXED of SAS; the model considered the TN pigs as no HS and the fixed effect of HS-sampling day was used to compare TN with HSd2 and HSd8. The AA composition of endogenous intestinal protein was not affected by HS (P > 0.10). The EIL of indispensable AA of TN, HSd2 and HSd8 pigs were: Arg, 314, 345, 335; His, 144, 163, 153; Ile, 169, 196, 173; Leu, 378, 434, 387; Lys, 238, 275, 250; Met, 099, 113, 110; Phe, 298, 337, 296; Thr, 489, 533, 481; Val, 335, 354, 343 mg/d, respectively. The EIL of dispensable AA of TN, HSd2and HSd8 pigs were: Ala, 377, 423, 383; Asp, 639, 684, 621; Glu, 478, 553, 509; Gly, 977, 838, 872; Pro, 763, 892, 1,941; Ser, 375, 394, 422; Tyr, 219, 251, 227 mg/d, respectively. The EIL of Thr and Phe tended to be increased (P ≤ 0.10), and Arg and His were enhanced at HSd2 (P < 0.05), and Pro increased at HSd8 (P = 0.01) compared with TN conditions. The EIL of the remainder AA was not affected by HS. Although HS increased the EIL of Arg and His within the first 2 d, it appears that normal EIL of AA is quickly reestablished. In summary, HS does not appear to affect the AA composition of intestinal endogenous proteins and suggest that the EIL of AA may not be critical in chronic HS pigs.