In the present experiment, zinc bacitracin was the least effective of three antibiotics in improving the performance of weanling pigs. This finding is consistent with that of Hays and Muir (1979) who reported that bacitracin ranked eighth out of eleven antibiotics in its ability to improve the growth performance of weaner pigs. The failure of bacitracin to improve animal performance was likely due to its inability to reduce total bacteria counts in the intestine.