**Abstract**

The effects of some functional amino acids (AAs) such as arginine, threonine, and methionine on the development of immune and digestive capacities in poultry were reviewed. The information was examined analytically to identify the source of the AA requirements, growth potential, type of housing, and type and degree of immune challenge applied. Regardless of these factors, the level of functional AA required to stimulate the immune or digestive response was higher than that required to maximize the productive performance. The implications section describes the main obstacles to integrating and applying the concept of functional AA in conventional diet formulation, and its use in birds raised under commercial conditions experiencing different types and degrees of immune stressors. It is necessary to develop a profile of functional AAs and establish their strategic use during or after immunological challenge situations to aid in the recovery of productive parameters to prechallenge levels.

**Keywords:** functional amino acids, growth, immune response, digestive function
