To determine whether adult dogs are able to regulate their intake of protein, 2-year-old female Beagles were allowed self-selection from 2 diets that differed in concentration of protein. Such a feeding regimen permitted the dogs to select for protein without affecting energy intake. Within the 1st week of the 4-week study, the dogs had established their pattern of protein intake. They selected approximately 30% of metabolizable energy from protein. Adult female rats offered the same diets also selected 30% of metabolizable energy from protein. The results indicated that adult dogs are able to regulate protein and energy intake.