A study was conducted to compare the effects of an antibiotic growth promoter (flavomycin) and two herbal natural feed additives (garlic and thyme) with and without a xylanase-based enzyme complex in wheat-based diets on growth performance, carcass parameters, total plasma cholesterol concentration, intestinal traits and the dry matter content of excreta of broiler chickens. A total of 112 day-old male broiler chicks was randomly assigned to eight groups containing 14 chicks each and raised from 1 to 42 days of age. The control group received the wheat-soyabean meal basal diet. In the treatment groups the basal diet was supplemented with one of the following: an antibiotic, thyme, garlic, an enzyme, the antibiotic plus the enzyme, thyme plus the enzyme or garlic plus the enzyme. During the 42-d growth period there were no significant differences in body weight gain, feed intake and feed conversion ratio of the broilers between dietary treatments. Feeding the diet supplemented with the antibiotic plus the enzyme significantly increased hot and cold carcass yields compared to the diets supplemented with thyme, garlic, enzyme and garlic plus enzyme. Total plasma cholesterol concentration, the dry matter content of excreta and the relative weights of the heart, pancreas, liver, gizzard and spleen were not significantly influenced by dietary treatments. The relative weight of the small intestines of the broilers receiving the diets supplemented with the antibiotic, antibiotic plus enzyme, thyme plus enzyme and garlic plus enzyme were significantly less than those of the broilers fed the basal diet and the diets supplemented with thyme, garlic and enzyme. The basal diet and garlic supplemented diet significantly increased the length of the small intestine compared to the other dietary treatments. Broilers receiving the diet supplemented with antibiotic had significantly lower total aerobic bacterial counts in the small intestines compared to those on the other dietary treatments. The combined supplementation of the antibiotic and enzyme resulted in a significantly lower E. coli concentration in the small intestines compared to the basal diet and the other dietary treatments. © South African Society for Animal Science.