The relationship between stress and feed efficiency in finisher swine was investigated through an adrenocorticotropin hormone (ACTH) challenge. The objective of this study was to evaluate the role of the ACTH-cortisol axis and the stress response in feed efficiency using pigs divergently selected for RFI. Gilts divergently selected for residual feed intake (RFI) were used as a model for feed efficiency and were challenged with 0.2 IU/kg BW of exogenous porcine ACTH. Serial blood samples were collected and plasma cortisol concentrations were determined. These results indicate that high-RFI pigs(lower feed efficiency) are more responsive to an ACTH challenge, but cope equally as well as pigs selected for low-RFI (higher feed efficiency).