An experiment was conducted to determine the effects of varying levels of dietary fat and protein in corn-soybean meal diets on body weight gain, feed consumption, and feed efficiency (gain:feed ratio) of Nicholas Large White male turkeys between 8 and 22 wk of age. Diets containing 0, 5, 10, or 15% added fat from one of three sources and 18, 21, or 24% protein were fed. At 12 and 16 wk of age, protein levels of all diets were decreased by 2%. A total of 917 turkeys in 36 pens was used. Additions of 5, 10, and 15% fat increased body weight gains 3.3, 7.5, and 6.0%, respectively. Feed consumption decreased 1.3% and feed efficiency increased 2.1% for each 1% fat added to the standard and high protein diets. The fat containing 15% free fatty acids and 1.5% moisture, impurities, and unsaponifiables (MIU) decreased feed consumption 1.5% and increased feed efficiency 2.3% for each 1% added fat, and the two fat sources containing 48% free fatty acids and 5% MIU decreased feed consumption 1.2 or 1.1% and increased feed efficiency 2.1 or 2.0% for each 1% added fat. The former fat source was estimated to contain 7.7% more metabolizable energy than the average of the latter two fat sources. Cumulative body weight gain, feed consumption, and feed efficiency decreased 13.2, 5.7, and 8.1%, respectively, from feeding low protein diets in comparison with results of feeding standard and high protein diets. Maximum increases in body weight gains were obtained with 10% added fat at all levels of protein.(ABSTRACT TRUNCATED AT 250 WORDS)