Technical reports have indicated that the optimum levels of protein feeds for growth of intensively-cultured channel catfish has ranged from 25 to 40 percent. These conclusions are based on specific percentages of protein found best for growth or profit under experimental conditions. The most important factors affecting the growth response of channel catfish to feeds containing different levels of protein are: 1) size of fish, 2) water temperature, 3) natural food available, 4) daily feed allowance, 5) amount of non-protein energy in the feed, and 6) quality of the protein. These factors, based on various experiments, are detailed in this report. All are found to have a great influence on the percentage of protein thought best for catfish feeds, and each must be considered when interpreting research data or developing productive rations.