Two identical trials, each with 128 crossbred weanling barrows (6.8 +/- .2 and 7.6 +/- .2 kg for Trials 1 and 2, respectively), were conducted. In each trial, pigs were allowed to consume ad libitum a 16% CP corn-soybean meal basal diet (B), B + 55 ppm of carbadox, B + 250 ppm of copper (Cu), or B + 125 ppm of Yucca shidigera extract for 56 d (four pens/diet; eight pigs/pen). At d 56 of the test, eight pigs/diet (two pigs/pen) were slaughtered for carcass and viscera measurements. Data of carbadox treatment in Trial 1 are excluded from this paper because of an error in mixing of the diet. In Trial 1, during the test period from d 0 to 28, pigs fed Cu had greater (P < .05) ADG and ADFI than those fed B, whereas pigs fed yucca extract had higher ADFI (P < .05) but similar ADG (P > .05) compared with those fed B. During the period from 29 to 56 d, ADG was similar among pigs fed different diets (P > .05) but ADFI was affected (P < .05) by diet (yucca extract > Cu > B). No differences (P > .05) among diets were detected for gain/feed (G/F) and visceral weights expressed as a percentage of slaughter BW. In Trial 2, during the first 28 d, the ADG, ADFI, and G/F responses of pigs to Cu, yucca extract, and B were similar to those observed in Trial 1.(ABSTRACT TRUNCATED AT 250 WORDS)